AU2012244165B2 - Herbicide-resistant sunflower plants, polynucleotides encoding herbicide-resistant acetohydroxyacid synthase large subunit proteins, and methods of use - Google Patents

Abstract

Abstract Herbicide-resistant sunflower plants, isolated polynucleotides that encode herbicide-resistant and wild-type acetohydroxyacid synthase large subunit (AHASL) polypeptides, and the amino acid sequences of these polypeptides, are described. Expression cassettes and transformation vectors comprising the polynucleotides of the invention, as well as plants and host cells transformed with the polynucleotides, are described. Methods of using the polynucleotides to enhance the resistance of plants to herbicides, and methods for controlling weeds in the vicinity of herbicide-resistant plants are also described.

Description

Pool Section 29 Regulation 3.2(2) AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Herbicide-resistant sunflower plants, polynucleotides encoding herbicide-resistant acetohydroxyacid synthase large subunit proteins, and methods of use The following statement is a full description of this invention, including the best method of performing it known to us: P111AHAU/0710 HERBICIDE-RESISTANT SUNFLOWER PLANTS, POLYNUCLEOTIDES ENCODING HERBICIDE-RESISTANT ACETOHYDROXYACID SYNTHASE LARGE SUBUNIT PROTEINS, AND METHODS OF USE 5 FIELD OF THE INVENTION This invention relates to the field of agricultural biotechnology, particularly to herbicide-resistant sunflower plants and novel polynucleotide sequences that encode wild-type and herbicide-resistant sunflower acetohydroxyacid synthase large subunit 10 proteins. BACKGROUND OF THE INVENTION Acetohydroxyacid synthase (AHAS; EC 4.1.3.18, also known as acetolactate synthase or ALS), is the first enzyme that catalyzes the biochemical synthesis of the 15 branched chain amino acids valine, leucine and isoleucine (Singh (1999) "Biosynthesis of valine, leucine and isoleucine," in PlantAmino Acid, Singh, B.K., ed., Marcel Dekker Inc. New York, New York, pp. 227-247). AHAS is the site of action of five structurally diverse herbicide families including the sulfonylureas (Tan et al. (2005) Pest Manag. Sci. 61:246-57; Mallory-Smith and Retzinger (2003) Weed Technology 17:620-626; LaRossa 20 and Falco (1984) Trends Biotechnol. 2:158-161), the imidazolinones (Shaner et al. (1984) Plant Physiol. 76:545-546), the triazolopyrimidines (Subramanian and Gerwick (1989) "Inhibition of acetolactate synthase by triazolopyrimidines," in Biocatalysis in AgriculturalBiotechnology, Whitaker, J.R. and Sonnet, P.E.. eds., ACS Symposium Series, American Chemical Society, Washington, D.C., pp. 277-288), the 25 pyrimidinyloxybenzoates (Subramanian et al. (1990) Plant Physiol. 94: 239-244) and the sulfonylamino-carbonyltriazolinones (Tan et al. (2005) Pest Manag. Sci. 61:246-57; Mallory-Smith and Retzinger (2003) Weed Technology 17:620-626). Imidazolinone and sulfonylurea herbicides are widely used in modem agriculture due to their effectiveness at very low application rates and relative non-toxicity in animals, By inhibiting AHAS 30 activity, these families of herbicides prevent further growth and development of susceptible plants including many weed species. Several examples of commercially available imidazolinone herbicides are PURSUIT® (imazethapyr), SCEPTER® (imazaquin) and ARSENAL® (imazapyr). Examples of sulfonylurea herbicides are chlorsulfuron, metsulfuron methyl, sulfometuron methyl, chlorimuron ethyl, -1 thifensulfuron methyl, tribenuron methyl, bensulfuron methyl, nicosulfuron, ethametsulfuron methyl, rimsulfuron, triflusulfuron methyl, triasulfuron, primisulfuron methyl, cinosulfuron, amidosulfluon, fluzasulfuron, imazosulfuron, pyrazosulfuron ethyl and halosulfuron. 5 Due to their high effectiveness and low-toxicity, imidazolinone herbicides are favored for application by spraying over the top of a wide area of vegetation. The ability to spray a herbicide over the top of a wide range of vegetation decreases the costs associated with plant establishment and maintenance, and decreases the need for site preparation prior to use of such chemicals. Spraying over the top of a desired tolerant 10 species also results in the ability to achieve maximum yield potential of the desired species due to the absence of competitive species. However, the ability to use such spray over techniques is dependent upon the presence of imidazolinone-resistant species of the desired vegetation in the spray over area. Among the major agricultural crops, some leguminous species such as soybean 15 are naturally resistant to imidazolinone herbicides due to their ability to rapidly metabolize the herbicide compounds (Shaner and Robinson (1985) Weed Sci. 33:469 471). Other crops such as corn (Newhouse et al. (1992) Plant Physiol. 100:882-886) and rice (Barrett et al. (1989) Crop Safenersfor Herbicides, Academic Press, New York, pp. 195-220) are somewhat susceptible to imidazolinone herbicides. The differential 20 sensitivity to the imidazolinone herbicides is dependent on the chemical nature of the particular herbicide and differential metabolism of the compound from a toxic to a non toxic form in each plant (Shaner et al. (1984) Plant Physiol. 76:545-546; Brown et al., (1987) Pestic. Biochem. Physiol. 27:24-29). Other plant physiological differences such as absorption and translocation also play an important role in sensitivity (Shaner and 25 Robinson (1985) Weed Sci, 33:469-471). Plants resistant to imidazolinones, sulfonylureas, triazolopyrimidines, and pyrimidinyloxybenzoates have been successfully produced using seed, microspore, pollen, and callus mutagenesis in Zea mays, Arabidopsis thaliana, Brassica napus (i.e., canola) Glycine max, Nicotiana tabacum, sugarbeet (Beta vulgaris) and Oryza sativa 30 (Sebastian et aL. (1989) Crop Sci. 29:1403-1408; Swanson et al., 1989 Theor. Apple. Genet. 78:525-530; Newhouse et aL. (1991) Theor. AppL. Genet. 83:65-70; Sathasivan et al. (1991) Plant Physiol. 97:1044-1050; Mourand et aL. (1993) J. Heredity 84:91-96; Wright and Penner (1998) Theor. Apple. Genet. 96:612-620; U.S. Patent No. 5,545,822). In all cases, a single, partially dominant nuclear gene conferred resistance. Four -2imidazolinone resistant wheat plants were also previously isolated following seed mutagenesis of Triticum aestivum L. cv. Fidel (Newhouse et al. .(1992) Plant Physiol. 100:882-886). Inheritance studies confirmed that a single, partially dominant gene conferred resistance. Based on allelic studies, the authors concluded that the mutations in 5 the four identified lines were located at the same locus. One of the Fidel cultivar resistance genes was designated FS-4 (Newhouse et al. (1992) Plant Physiol. 100:882 886). Naturally occurring plant populations that were discovered to be resistant to imidazolinone and/or sulfonylurea herbicides have also been used to develop herbicide 10 resistant sunflower breeding lines. Recently, two sunflower lines that are resistant to a sulfonylurea herbicide were developed using germplasm originating from a wild population of common sunflower (Helianthus annuus) as the source of the herbicide resistance trait (Miller and Al-Khatib (2004) Crop Sci. 44:1037-1038). Previously, White et al. ((2002) Weed Sci. 50:432-437) had reported that individuals from a wild population 15 of common sunflower from South Dakota, U.S.A. were cross-resistant to an imidazolinone and a sulfonylurea herbicide. Analysis of a portion of the coding region of the acetohydroxyacid synthase large subunit (AHASL) genes of individuals from this population revealed a point mutation that results in an Ala-to-Val amino acid substitution in the sunflower AHASL protein that corresponds to Alanzs in the wild-type Arabidopsis 20 thaliana AHASL protein (White et al. (2003) WeedSci. 51:845-853). Earlier, Al-Khatib and Miller ((2000) Crop Sci. 40:869) reported the production of four imidazolinone resistant sunflower breeding lines. Computer-based modeling of the three dimensional conformation of the AHAS inhibitor complex predicts several amino acids in the proposed inhibitor binding pocket as 25 sites where induced mutations would likely confer selective resistance to imidazolinones (Ott et al, (1996) J. Mol. Biol. 263:359-368). Tobacco plants produced with some of these rationally designed mutations in the proposed binding sites of the AHAS enzyme have in fact exhibited specific resistance to a single class of herbicides (Ott et al. (1996) J Mol. Biol. 263:359-368). 30 Plant resistance to imidazolinone herbicides has also been reported in a number of patents. U.S. Patent Nos. 4,761,373, 5,331,107, 5,304,732, 6,211,438, 6,211,439 and 6,222,100 generally describe the use of an altered AHAS gene to elicit herbicide resistance in plants, and specifically discloses certain imidazolinone resistant corn lines. U.S. Patent No. 5,013,659 discloses plants exhibiting herbicide resistance due to -3mutations in at least one amino acid in one or more conserved regions. The mutations described therein encode either cross-resistance for imidazolinones and sulfonylureas or sulfonylurea-specific resistance, but imidazolinone-specific resistance is not described. U.S. Patent No. 5,731,180 and U.S. Patent No. 5,767,361 discuss an isolated gene having 5 a single amino acid substitution in a wild-type monocot AHAS amino acid sequence that results in imidazolinone-specific resistance. In addition, rice plants that are resistant to herbicides that interfere with AHAS have been developed by mutation breeding and also by the selection of herbicide-resistant plants from a pool of rice plants produced by anther culture. See, U.S. Patent Nos. 5,545,822, 5,736,629, 5,773,703, 5,773,704, 5,952,553 and 10 6,274,796. In plants, as in all other organisms examined, the AHAS enzyme is comprised of two subunits: a large subunit (catalytic role) and a small subunit (regulatory role) (Duggleby and Pang (2000) J. Biochem. Mol. Bio. 33:1-36). The AHAS large subunit (also referred to herein as AHASL) may be encoded by a single gene as in the case of 15 Arabidopsis, and sugar beet or by multiple gene family members as in maize, canola, and cotton. Specific, single-nucleotide substitutions in the large subunit confer upon the enzyme a degree of insensitivity to one or more classes of herbicides (Chang and Duggleby (1998) Biochem J. 333:765-777). For example, bread wheat, Triticun aestivun L., contains three homoeologous 20 acetohydroxyacid synthase large subunit genes. Each of the genes exhibit significant expression based on herbicide response and biochemical data from mutants in each of the three genes (Ascenzi et al. (2003) International Society of Plant Molecular Biologists Congress, Barcelona, Spain, Ref. No. S10-17). The coding sequences of all three genes share extensive homology at the nucleotide level (WO 03/014357). Through sequencing 25 the AHASL genes from several varieties of Triticum aestivum, the molecular basis of herbicide tolerance in most IMI-tolerant (imidazolinone-tolerant) lines was found to be the mutation S653(At)N, indicating a seine to asparagine substitution at a position equivalent to the seine at amino acid 653 in Arabidopsis thaliana (WO 03/0143 6; WO 03/014357). This mutation is due to a single nucleotide polymorphism (SNP) in the DNA 30 sequence encoding the AHASL protein. Multiple AHASL genes are also know to occur in dicotyledonous plants species. Recently, Kolkman et al. ((2004) Theor, Appl. Genet. 109: 1147-1159) reported the identification, cloning, and sequencing for three AHASL genes (AHASLI, AJHASL2, and AHASL3) from herbicide-resistant and wild type genotypes of sunflower (Helianthus -4annuus L.). Kolkman et al reported that the herbicide-resistance was due either to the Prol97Leu (using the Arabidopsis AHASL amino acid position nomenclature) substitution or the Ala205Val substitution in the AHASLI protein and that each of these substitutions provided resistance to both imidazolinone and sulfonylurea herbicides. 5 Given their high effectiveness and low-toxicity, imidazolinone herbicides are favored for agricultural use. However, the ability to use imidazolinone herbicides in a particular crop production system depends upon the availability of imidazolinone resistant varieties of the crop plant of interest. To produce such imidazolinone-resistant varieties, plant breeders need to develop breeding lines with the imidazolinone-resistance 10 trait. Thus, additional imidazolinone-resistant breeding lines and varieties of crop plants, as well as methods and compositions for the production and use of imidazolinone resistant breeding lines and varieties, are needed SUMMARY OF THE INVENTION 15 The present invention provides sunflower plants having increased resistance to herbicides when compared to a wild-type sunflower plant. In particular, the sunflower plants of the invention have increased resistance to imidazolinone herbicides, when compared to a wild-type sunflower plant. The herbicide-resistant sunflower plants of the invention comprise at least one copy of a gene or polynucleotide that encodes a herbicide 20 resistant acetohydroxyacid synthase large subunit (AHASL). Such a herbicide-resistant AHASL protein comprises a threonine at amino acid position 107 or equivalent position. A herbicide-resistant sunflower plant of the invention can contain one, two, three, four, five, six, or more copies of a gene or polynucleotide encoding a herbicide-resistant AHASL protein of the invention. The sunflower plants of the invention also include 25 seeds and progeny plants that comprise at least one copy of a gene or polynucleotide encoding a herbicide-resistant AHASL protein of the invention. In one embodiment, the present invention provides herbicide-resistant sunflower plants of a sunflower line that is designated herein as S4897 and progeny and derivatives thereof that comprise the herbicide resistance characteristics of S4897. A genetic line 30 designated herein as GM40 was derived from, and possesses the herbicide resistance characteristics of S4897. A sample of seeds of the GM40 line has been deposited with the American Type Culture Collection (ATCC) as ATCC Patent Deposit No. PTA-6716. Thus, a sunflower plant of the invention that comprises the herbicide resistance characteristics of GM40 or a sunflower plant having ATCC Patent Deposit No. PTA -5- 6716 also comprises the herbicide resistance characteristics of S4897. S4897 sunflower plants, GM40 sunflower plants, and sunflower plants having ATCC Patent Deposit No. PTA-6716 and progeny and derivatives thereof comprising the herbicide resistance characteristics of S4897, GM40, or a sunflower plant having ATCC Patent Deposit No. 5 PTA-6716, comprise in their genomes an AHASL1 gene that comprises the nucleotide sequence set forth in SEQ ID NO: 1 and that encodes the AHASLI protein comprising, the amino acid sequence set forth in SEQ ID NO: 2. When compared to the amino acid sequence of the AHASLI protein (SEQ ID NO: 4) that is encoded by an AHASL1 gene (SEQ ID NO: 3) from a wild-type sunflower plant, the amino acid sequence set forth in 10 SEQ ID NO: 2 has a single amino acid difference from the wild-type amino acid sequence. In the amino acid sequence set forth in SEQ ID NO: 2, there is threonine at amino acid position 7. This position corresponds to position 107 in the full-length sunflower AHASLI protein encoded by the nucleotide sequence set forth in SEQ ID NO: 12 (Accession No. AY54145 1). In the wild-type AHASLI amino acid sequence of 15 the invention (SEQ ID NO: 4), this equivalent amino acid position has an alanine. Unless otherwise indicated, the amino acid positions referred to herein for sunflower AHASL proteins correspond to the amino acid positions of the full-length amino acid sequence set forth in SEQ ID NO: 12. . In another embodiment, the present invention provides herbicide-resistant 20 sunflower plants that are sunflower line that is designated herein as GM1606. A sample of seeds of genetic material of GM1606 has been deposited with the ATCC as ATCC Patent Deposit No. PTA-7606. Thus, the present invention provides herbicide-resistant sunflower plants that having ATCC Patent Deposit No. PTA-7606 and progeny and derivatives thereof that comprise the herbicide resistance characteristics of the sunflower 25 plants having ATCC Patent Deposit No. PTA-7606. Like the S4897 and GM40 sunflower plants, GM1606 and progeny and derivatives thereof comprising the herbicide resistance characteristics of GM1 606 comprise in their genomes an AHASL1 gene encodes an AHASLI protein comprising a threonine at position 107 in the full-length sunflower AHASLI protein. Similarly, sunflower plants having ATCC Patent Deposit 30 No. PTA-7606, and progeny and deriviatives thereof comprising the herbicide resistance characteristics of the sunflower plants having ATCC Patent Deposit No. PTA-7606 comprise in their genomes an AHASLJ gene encodes an AHASLI protein comprising a threonine at position 107 in the full-length sunflower AHASLI protein. -6- The present invention further provides isolated polynucleotides and isolated polypeptides for sunflower (Helianthus annuus) AHASL proteins. The polynucleotides of the invention encompass nucleotide sequences that encode herbicide-resistant and wild type AHASL proteins, including, but not limited to, the proteins encoded by the 5 sunflower AHASLI, AHASL2, and AHASL3 genes. The herbicide-resistant sunflower AHASL proteins of the invention are imidazolinone-resistant AHASL proteins that comprise an amino acid other than alanine at position 107 of a full-length sunflower AHASL 1 protein or equivalent position. Preferably, the amino acid at position 107 or equivalent position is a threonine. The polynucleotides of the invention encompass the 10 nucleotide sequences set forth in SEQ ID NOS: I and 3, nucleotide sequences encoding the amino acid sequences set forth in SEQ ID NOS: 2 and 4, and fragments and variants of said nucleotide sequences that encode proteins comprising AHAS activity. The present invention provides expression cassettes for expressing the polynucleotides of the invention in plants, plant cells, and other, non-human host cells. 15 The expression cassettes comprise a promoter expressible in the plant, plant cell, or other host cells of interest operably linked to a polynucleotide of the invention that encodes either a wild-type or herbicide-resistant AHASL protein. If necessary for targeting expression to the chloroplast, the expression cassette can also comprise an operably linked chloroplast-targeting sequence that encodes of a chloroplast transit peptide to 20 direct an expressed AHASL protein to the chloroplast The expression cassettes of the invention find use in a method for enhancing the herbicide tolerance of a plant and a host cell, The method involves transforming the plant or host cell with an expression cassette of the invention, wherein the expression cassette comprises a promoter that is expressible in the plant or host cell of interest and the promoter is operably linked to a polynucleotide 25 of the invention that encodes an herbicide-resistant AHASL protein of the invention. The method further comprises regenerating a transformed plant from the transformed plant cell. The present invention provides a method for increasing AHAS activity in a plant comprising transforming a plant cell with a polynucleotide construct comprising a 30 nucleotide sequence operably linked to a promoter that drives expression in a plant cell and regenerating a transformed plant from the transformed plant cell. The nucleotide sequence is selected from those nucleotide sequences that encode the herbicide-resistant or wild-type AHASL proteins of the invention, particularly the nucleotide sequences set forth in SEQ ID NOS: 1 and 3, and nucleotide sequences encoding the amino acid -7sequences set forth in SEQ ID NOS: 2, and 4, and fragments and variants thereof. A plant produced by this method comprises increased AHAS activity or increased herbicide-resistant AHAS activity, when compared to an untransformed plant. The present invention provides a method for producing a herbicide-resistant plant 5 comprising transforming a plant cell with a polynucleotide construct comprising a nucleotide sequence operably linked to a promoter that drives expression in a plant cell and regenerating a transformed plant from said transformed plant cell. The nucleotide sequence is selected from those nucleotide sequences that encode the herbicide-resistant AHASL proteins of the invention, particularly the nucleotide sequence set forth in SEQ 10 ID NO: 1, the nucleotide sequence encoding the amino acid sequence set forth in SEQ ID NO: 2, and fragments and variants thereof, A herbicide-resistant plant produced by this method comprises enhanced resistance to at least one herbicide, particularly an imidazolinone herbicide, when compared to an untransformed plant. The present invention provides a method for enhancing herbicide-tolerance in a 15 herbicide-tolerant plant. The method finds use in enhancing the resistance of a plant that already is resistant to a level of a herbicide that would kill or significantly injure a wild type plant. Such a herbicide-tolerant plant can be a herbicide-tolerant plant that has been genetically engineered for herbicide-tolerance or a herbicide-tolerant plant that was developed by means that do not involve recombinant DNA such as, for example, the 20 S4897, GM40, and GM1 606 sunflower plants of the present invention. The method comprises transforming a herbicide-tolerant plant with a polynucleotide construct comprising a nucleotide sequence operably linked to a promoter that drives expression in a plant cell and regenerating a transformed plant from the transformed plant cell. The nucleotide sequence is selected from those nucleotide sequences that encode the 25 herbicide-resistant AHASL proteins of the invention, particularly a nucleotide sequence comprising the nucleotide sequence set forth in SEQ ID NO: 1, nucleotide sequences encoding an amino acid sequence comprising the amino acid sequence set forth in SEQ ID NO: 2, and fragments and variants thereof. The present invention provides transformation vectors comprising a selectable 30 marker gene of the invention. The selectable marker gene comprises a promoter that drives expression in a host cell operably linked to a polynucleotide comprising a nucleotide sequence that encodes an herbicide-resistant AHASL protein of the invention. The transformation vector can additionally comprise a gene of interest to be expressed in -8the host cell and can also, if desired, include a chloroplast-targeting sequence that is operably linked to the polynucleotide of the invention. The present invention further provides methods for using the transformation vectors of the invention to select for cells transformed with the gene of interest. Such 5 methods involve the transformation of a host cell with the transformation vector, exposing the cell to a level of an imidazolinone herbicide that would kill or inhibit the growth of a non-transformed host cell, and identifying the transformed host cell by its ability to grow in the presence of the herbicide. In one embodiment of the invention, the host cell is a plant cell and the selectable marker gene comprises a promoter that drives 10 expression in a plant cell. The present invention provides a method for controlling weeds in the vicinity of the herbicide-resistant plants of the invention, including the herbicide-resistant sunflower plants described above and plants transformed with the herbicide-resistant AHASL polynucleotides of the invention. Such transformed plants comprise in their genomes at 15 least one expression cassette comprising a promoter that drives gene expression in a plant cell, wherein the promoter is operably linked to an AHASL polynucleotide of the invention. The method comprises applying an effective amount of an herbicide to the weeds and to the herbicide-resistant plant, wherein the herbicide-resistant plant has increased resistance to at least one herbicide, particularly an imidazolinone herbicide, 20 when compared to a wild-type or untransformed plant. The plants of the present invention can be transgenic or non-transgenic. An example of a non-transgenic sunflower plant having increased resistance to imidazolinone and/or sulfonylurea herbicides includes S4897, GM40, or GM 1606 sunflower plants and sunflower plants having ATCC Patent Deposit No. PTA-6716 or PTA-7606; or mutant, 25 recombinant, or a genetically engineered derivative of and S4897, GM40, or GM1606, the sunflower plant having ATCC Patent Deposit No. PTA-6716 or PTA-7606, or two of more of S4897, GM40, GM1606, the sunflower plant having ATCC Patent Deposit No. PTA-6716, and the sunflower plant having ATCC Patent Deposit No. PTA-7606; or of any progeny of S4897, GM40, or GM 1606, the sunflower plant having ATCC Patent 30 Deposit No. PTA-6716 or PTA-7606, or two of more of S4897, GM40, GM1606, the sunflower plant having ATCC Patent Deposit No. PTA-6716, and the sunflower plant having ATCC Patent Deposit No. PTA-7606; or a plant that is a progeny of any of these plants; or a plant that comprises the herbicide resistance characteristics of S4897, GM40, -9- GM1606, the sunflower plant having ATCC Patent Deposit No. PTA-6716, and/or the sunflower plant having ATCC Patent Deposit No. PTA-7606, The present invention also provides plants, plant organs, plant tissues, plant cells, seeds, and non-human host cells that are transformed with the at least one polynucleotide, 5 expression cassette, or transformation vector of the invention. Such transformed plants, plant organs, plant tissues, plant cells, seeds, and non-human host cells have enhanced tolerance or resistance to at least one herbicide, at levels of the herbicide that kill or inhibit the growth of an untransformed plant, plant tissue, plant cell, or non-human host cell, respectively. Preferably, the transformed plants, plant tissues, plant cells, and seeds 10 of the invention are Arabidopsis thaliana, sunflower, and other crop plants. The present invention further provides isolated polypeptides comprising imidazolinone-resistant and wild-type sunflower AHASL proteins. The isolated polypeptides comprise the amino acid sequences set forth in SEQ ID NOS: 2 and 4, the amino acid sequences encoded by nucleotide sequences set forth in SEQ ID NOS: 1 and 15 3, and fragments and variants of said amino acid sequences that encode proteins comprising AHAS activity. BRIEF DESCRIPTION THE DRAWINGS Figure 1 is a nucleotide sequence alignment of the nucleotide sequences of the 20 herbicide-resistant sunflower AHASL1 gene (SEQ ID NO: 1), the wild-type sunflower AHASLI gene (SEQ ID NO: 3), GenBank Accession No. U16280 (SEQ ID NO: 5), GenBank Accession No, AY541451 (SEQ ID NO: 11) and GenBank Accession No. AY124092 (SEQ ID NO: 13). The site of the mutation in (SEQ ID NO: 1) is indicated by an asterisk. The mutation is a G-to-A transition at nucleotide position 21 of SEQ ID 25 NO: 1, Figure 2 is an amino acid sequence alignment of the herbicide-resistant sunflower AHASLI protein (SEQ ID NO: 2), the wild-type sunflower AHASLI protein (SEQ ID NO: 4), GenBank Accession No. U16280 (SEQ ID NO: 6), GenBank Accession No. AY541451 (SEQ ID NO: 12), and GenBank Accession No. AY124092 (SEQ ID NO: 14) 30 . The asterisk indicates the site of the single amino acid substitution (Ala-to-Thr) found in the herbicide-resistant sunflower AHASLI protein. This site of the substitution corresponds to amino acid position 7 in the partial-length AHASLI amino acid sequence set forth in SEQ ID NO: 2. The equivalent position of this substitution in the full-length sunflower AHASL1 amino acid sequence set forth in SEQ ID NO: 12 is 107. -10- Figure 3 is a photographic illustration demonstrating the increased herbicide tolerance of S4897 sunflower plants (right side) plants as compared to the herbicide tolerant IMISUN-1 sunflower plants (Al-Khatib and Miller (2000) Crop Sci. 40:869-870) in a greenhouse study. The 84897 and IMISUN-l sunflower plants were spray-treated 5 with imazamox at rate of 200 g ai/ha. Control, wild-type sunflower plants did not survive following the spray treatment with imazamox at a rate of either 100 or 200 g ai/ha (not shown). The photograph was taken a few days after the plants were spray treated, Figure 4 is graphical illustration of herbicide injury in a greenhouse test following the spray treatment of IMISUN-1, wild-type, and S4897 sunflower plants with imazamox 10 at either 100 (light columns) or 200 g ai/ ha (dark columns). This figure demonstrates that the S4897 herbicide-resistance sunflower plants have a significantly greater resistance or tolerance to two rates of imazamox when compared either the herbicide resistant IMISUN-1 plants and wild-type plants. Herbicide injury was evaluated 17 days after the imazamox application. The IMISUN-1 plants are known to possess an alanine 15 to-valine substitution at amino acid 190 (Kolkman et al. (2004) Theor. Apple. Genet, 109: 1147-1159). Figure 5 is a photographic illustration demonstrating the increased herbicide tolerance of S4897 sunflower plants (right side) as compared to the herbicide-tolerant IMISUN-1 sunflower plants in the greenhouse trial described in Example 4. 20 Figure 6 is a photographic illustration demonstrating the increased herbicide tolerance of S4897 sunflower plants as compared to Clearfield@ Variety A sunflower plants in the greenhouse trial described in Example 5. Figure 7 is graphical illustration of a comparison of the inhibition of AHAS by Raptor for a non-Clearfield variety, a Clearfield variety and 54897 sunflower plants as 25 described in Example 5. Figure 8 is graphical illustration of a comparison of the inhibition of AHAS by Glean for a non-Clearfield variety, a Clearfield variety and S4897 sunflower plants as described in Example 5. Figure 9 is a graphical illustration of the effect of foliar application of imazapir on 30 plant height 14 days after treatment for two mutants of sunflower, Mean height (% of untreated plots) are represented by squares and error bars represent the standard deviation of the means. Figure 10 is a graphical illustration of the effect of foliar application of imazapir on Phytotoxicity Index (PI) 14 days after treatment for two mutants of sunflower. Mean - 11 - PI are represented by squares and error bars represent the standard deviation of the means. Figure 11 is a graphical illustration of the effect of foliar application of imazapir 5 on biomass accumulation 14 days after treatment for two mutants of sunflower. Mean dry biomass (% of untreated plots) are represented by squares and error bars represent the standard deviation of the means. Figure 12 is a graphical illustration of the effect of foliar application of imazapir on root biomass 14 days after treatment for two mutants of sunflower. Mean root dry 10 mass (% of untreated plots) are represented by squares and error bars represent the standard deviation of the means. SEQUENCE LISTING The nucleotide and amino acid sequences listed in the accompanying sequence 15 listing are shown using standard letter abbreviations for nucleotide bases, and three-letter code for amino acids. The nucleotide sequences follow the standard convention of beginning at the 5' end of the sequence and proceeding forward (i.e., from left to right in each line) to the 3' end. Only one strand of each nucleic acid sequence is shown, but the complementary strand is understood to be included by any reference to the displayed 20 strand. The amino acid sequences follow the standard convention of beginning at the amino terminus of the sequence and proceeding forward (i.e., from left to right in each line) to the carboxy terminus. SEQ ID NO: 1 sets forth the partial-length nucleotide sequence encoding a herbicide-resistant AHASLI protein from the sunflower line S4897. 25 SEQ ID NO: 2 sets forth the partial-length amino acid sequence of the herbicide resistant AHASL 1 protein encoded by the nucleotide sequence set forth in SEQ ID NO: 1. SEQ ID NO: 3 sets forth the partial-length nucleotide sequence encoding the wild type AHASLI protein from sunflower line BTK47. 30 SEQ ID NO: 4 sets forth the partial-length amino acid sequence of the wild-type AHASLI protein encoded by the nucleotide sequence set forth SEQ ID NO: 3. SEQ ID NO: 5 is the nucleotide sequence of GenBank Accession No. U16280. SEQ ID NO: 6 is the amino acid sequence encoded by the nucleotide sequence of GenBank Accession No, U16280. - 12- SEQ ID NO: 7 sets forth the nucleotide sequence of the HA1U409 primer that is described in Example 2. SEQ ID NO: 8 sets forth the nucleotide sequence of the HA1L1379 primer that is described in Example 2. 5 SEQ ID NO: 9 sets forth the nucleotide sequence of the HA1U1313 primer that is described in Example 2. SEQ ID NO: 10 sets forth the nucleotide sequence of the HA1L2131 primer that is described in Example 2. SEQ ID NO: 11 is the nucleotide sequence of GenBank Accession No. 10 AY541451. SEQ ID NO: 12 is the amino acid sequence encoded by the nucleotide sequence of GenBank Accession No. AY541451. SEQ ID NO: 13 is the nucleotide sequence of GenBank Accession No. AY124092. 15 SEQ ID NO: 14 is the amino acid sequence encoded by the nucleotide sequence of GenBank Accession No. AY124092. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to sunflower plants having increased resistance to 20 herbicides when compared to a wild-type sunflower plant. Herbicide-resistant sunflower plants were produced as described hereinbelow by exposing wild-type (with respect to herbicide resistance) sunflower plants to a mutagen, allowing the plants to mature and reproduce, and selecting progeny plants that displayed enhanced resistance to an imidazolinone herbicide, relative to the resistance of a wild-type sunflower plant. The 25 invention provides the herbicide-resistant sunflower lines that are referred to herein as S4897, GM40, and GM1606. From the S4897 herbicide-resistant sunflower plants and BTK47 wild-type sunflower plants, the coding region of an acetohydroxyacid synthase large subunit gene (designated as AHASLI) was isolated by polymerase chain reaction (PCR) amplification 30 and sequenced. By comparing the polynucleotide sequences of the herbicide-resistant and wild-type sunflower plants, it was discovered that the coding region of the AHASL 1 polynucleotide sequence from the herbicide-resistant sunflower plant differed from the AHASL I polynucleotide sequence of the wild type plant by a single nucleotide, a G-to-A transition at nucleotide 21 (SEQ ID NO: 1). This G-to-A transition in the AHASL i - 13 polynucleotide sequence results in an alanine-to-threonine substitution at amino acid 7 (SEQ ID NO: 2) in a conserved region of the predicted amino acid sequence of the herbicide-resistant sunflower AHASLI protein (SEQ ID NO: 2), relative to the equivalent amino acid position of the wild-type AHASL 1 protein from sunflower line BTK47 (i.e., 5 amino acid 7 of SEQ ID NO: 4). Because the nucleotide sequence set forth in SEQ ID NO: 1 does not correspond to a full-length coding region of an AHASL protein, the amino acid sequence encoded thereby that is set forth in SEQ ID NO: 2 is also less than full-length. To facilitate comparison with other sunflower AHASL amino acid sequences, the amino acid positions 10 of sunflower AHASL proteins referred to herein, unless otherwise indicated or apparent for the context in which such positions appear, correspond to the amino acid positions of the full-length amino acid sequence of the sunflower AHASLI protein encoded by the nucleotide sequence having GenBank Accession No. AY541451 (SEQ ID NO: 12). Accordingly, the alanine-to-threonine substitution at amino acid position 7 of SEQ ID 15 NO: 2 corresponds to amino acid position 107 in the amino acid sequence of SEQ ID NO: 12. Thus, the present invention discloses an amino acid substitution that can be used to produce herbicide-resistant sunflower AHASL proteins, the polynucleotides encoding such proteins, and herbicide-resistant plants, plant tissues, plant cells, and seeds, Because 20 the alanine that is found at amino acid position 107 in wild-type, full-length sunflower AHASLI proteins or equivalent position is within a region of amino acids that is conserved across plant species, it is expected that the substitution of another amino acid, preferably threonine, for this same conserved alanine in other AHASL proteins from sunflower (e.g., AHASL2 and AHASL3) will also confer herbicide tolerance, Thus, a 25 polynucleotide encoding a sunflower AHASL protein can be mutated by any method known in the art such as, for example, site-directed mutagenesis to produce a sunflower polynucleotide that encodes an AHASL protein with a threonine at position 107 or equivalent position. Polynucleotide sequences and the amino acid sequences encoded thereby corresponding to the sunflower AHIASLJ, AHASL2, and AHASL3 genes are set 30 forth in GenBank Accession Nos. AY541451 (SEQ ID NOS: 11 and 12), AY541452, AY541453, AY541454, AY541455, AY541456, AY541457, and AY541458; all of which are herein incorporated by reference. Accordingly, such polynucleotides and the herbicide-resistant AHASL proteins encoded thereby find use in the production of -14herbicide-resistant plants, plant cells, plant tissues, and seeds by the methods disclosed herein. The present invention additionally encompasses isolated sunflower AHASL2 and AHASL3 polynucleotides that encode herbicide-resistant AHASL2 and AHASL3 5 proteins, respectively. Such herbicide-resistant AHASL2 and AHASL3 proteins each comprise an amino acid other than alanine at position 107 or equivalent position. Preferably in such herbicide-resistant AHASL2 and AHASL3 proteins, the amino acid at position 107 or equivalent position is threonine. The invention further relates to isolated polynucleotide molecules comprising 10 nucleotide sequences that encode acetohydroxyacid synthase large subunit (AHASL) proteins and to such AHASL proteins. The invention discloses the isolation and nucleotide sequence of a polynucleotide encoding a herbicide-resistant sunflower AHASLI protein from an herbicide-resistant sunflower plant that was produced by chemical mutagenesis of wild-type sunflower plants. The herbicide-resistant sunflower 15 AHASL1 proteins of the invention possess a alanine-to-threonine substitution at position 107 or equivalent position in their respective amino acid sequences, when compared to the corresponding wild-type amino acid sequence. The invention further discloses the isolation and nucleotide sequence of a polynucleotide molecule encoding a wild-type sunflower AHASLI protein. 20 The present invention provides isolated polynucleotide molecules that encode AHASL proteins from sunflower (Helianthus annuus L.). Specifically, the invention provides isolated polynucleotide molecules comprising: the nucleotide sequences set forth in SEQ ID NOS: 1 and 3, nucleotide sequences encoding AHASL proteins comprising the amino acid sequences set forth in SEQ ID NOS: 2 and 4, and fragments and variants of 25 such nucleotide sequences that encode functional AHASL proteins. The isolated herbicide-resistant AHASL polynucleotide molecules of the invention comprise nucleotide sequences that encode herbicide-resistant AHASL proteins. Such polynucleotide molecules can be used in polynucleotide constructs for the transformation of plants, particularly crop plants, to enhance the resistance of the plants to 30 herbicides, particularly herbicides that are known to inhibit AHAS activity, more particularly imidazolinone herbicides. Such polynucleotide constructs can be used in expression cassettes, expression vectors, transformation vectors, plasmids and the like. The transgenic plants obtained following transformation with such polynucleotide - 15constructs show increased resistance to AHAS-inhibiting herbicides such as, for example, imidazolinone and sulfonylurea herbicides. Compositions of the invention include nucleotide sequences that encode AH ASL proteins. In particular, the present invention provides for isolated polynucleotide 5 molecules comprising nucleotide sequences encoding the amino acid sequences shown in SEQ ID NOS: 2 and 4, and fragments and variants thereof that encode polypeptides comprising AHAS activity. Further provided are polypeptides having an amino acid sequence encoded by a polynucleotide molecule described herein, for example those set forth in SEQ ID NOS: 1 and 3, and fragments and variants thereof that encode 10 polypeptides comprising AHAS activity. The invention encompasses isolated or substantially purified nucleic acid or protein compositions. An "isolated" or "purified" polynucleotide molecule or protein, or biologically active portion thereof, is substantially or essentially free from components that normally accompany or interact with the polynucleotide molecule or protein as found 15 in its naturally occurring environment. Thus, an isolated or purified polynucleotide molecule or protein is substantially free of other cellular material, or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized. Preferably, an "isolated" nucleic acid is free of sequences (preferably protein encoding sequences) that naturally flank the nucleic 20 acid (i.e., sequences located at the 5' and 3' ends of the nucleic acid) in the genomic DNA of the organism from which the nucleic acid is derived. For example, in various embodiments, the isolated polynucleotide molecule can contain less than about 5 kb, 4 kb, 3 kb, 2 kb, I kb, 0.5 kb, or 0.1 kb of nucleotide sequences that naturally flank the polynucleotide molecule in genomic DNA of the cell from which the nucleic acid is 25 derived. A protein that is substantially free of cellular material includes preparations of protein having less than about 30%, 20%, 10%, 5%, or 1% (by dry weight) of contaminating protein. When the protein of the invention or biologically active portion thereof is recombinantly produced, preferably culture medium represents less than about 30%, 20%, 10%, 5%, or 1% (by dry weight) of chemical precursors or non-protein-of 30 interest chemicals. The present invention provides isolated polypeptides comprising AHASL proteins. The isolated polypeptides comprise an amino acid sequence selected from the group consisting of the amino acid sequences set forth in SEQ ID NOS: 2 and 4, the amino acid sequences encoded by nucleotide sequences set forth in SEQ ID NOS: 1 and -16- 3, and functional fragments and variants of said amino acid sequences that encode an AHASL polypeptide comprising AHAS activity. By "functional fragments and variants" is intended fragments and variants of the exemplified polypeptides that comprise AHAS activity. 5 In certain embodiments of the invention, the methods involve the use of herbicide tolerant or herbicide-resistant plants. By an "herbicide-tolerant" or "herbicide-resistant" plant, it is intended that a plant that is tolerant or resistant to at least one herbicide at a level that would normally kill, or inhibit the growth of, a normal or wild-type plant. In one embodiment of the invention, the herbicide-tolerant plants of the invention comprise 10 a herbicide-tolerant or herbicide-resistant AHASL protein. By "herbicide-tolerant AHASL protein" or "herbicide-resistant AHASL protein", it is intended that such an AHASL protein displays higher AHAS activity, relative to the AHAS activity of a wild type AHASL protein, when in the presence of at least one herbicide that is known to interfere with AHAS activity and at a concentration or level of the herbicide that is to 15 known to inhibit the AHAS activity of the wild-type AHASL protein. Furthermore, the AHAS activity of such a herbicide-tolerant or herbicide-resistant AHASL protein may be referred to herein as "herbicide-tolerant" or "herbicide-resistant" AHAS activity. For the present invention, the terms "herbicide-tolerant" and "herbicide-resistant" are used interchangeable and are intended to have an equivalent meaning and an 20 equivalent scope. Similarly, the terms "herbicide-tolerance" and "herbicide-resistance" are used interchangeable and are intended to have an equivalent meaning and an equivalent scope. Likewise, the terms "imidazolinone-resistant" and "imidazolinone resistance" are used interchangeable and are intended to be of an equivalent meaning and an equivalent scope as the terms "imidazolinone-tolerant" and "imidazolinone-tolerance", 25 respectively. The invention encompasses herbicide-resistant AHASL polynucleotides and herbicide-resistant AHASL proteins. By "herbicide-resistant AHASL polynucleotide" is intended a polynucleotide that encodes a protein comprising herbicide-resistant AHAS activity. By "herbicide-resistant AHASL protein" is intended a protein or polypeptide 30 that comprises herbicide-resistant AHAS activity. Further, it is recognized that a herbicide-tolerant or herbicide-resistant AHASL protein can be introduced into a plant by transforming a plant or ancestor thereof with a nucleotide sequence encoding a herbicide-tolerant or herbicide-resistant AHASL protein. Such herbicide-tolerant or herbicide-resistant AHASL proteins are encoded by the -17herbicide-tolerant or herbicide-resistant AHASL polynucleotides. Alternatively, a herbicide-tolerant or herbicide-resistant AHASL protein may occur in a plant as a result of a naturally occurring or induced mutation in an endogenous AHASL gene in the genome of a plant or progenitor thereof. 5 The present invention provides plants, plant tissues, plant cells, and host cells with increased resistance or tolerance to at least one herbicide, particularly an imidazolinone or sulfonylurea herbicide. The preferred amount or concentration of the herbicide is an "effective amount" or "effective concentration." By "effective amount" and "effective concentration" is intended an amount and concentration, respectively, that is sufficient to 10 kill or inhibit the growth of a similar, wild-type, plant, plant tissue, plant cell, or host cell, but that said amount does not kill or inhibit as severely the growth of the herbicide resistant plants, plant tissues, plant cells, and host cells of the present invention. Typically, the effective amount of a herbicide is an amount that is routinely used in agricultural production systems to kill weeds of interest. Such an amount is known to 15 those of ordinary skill in the art. By "similar, wild-type, plant, plant tissue, plant cell or host cell" is intended a plant, plant tissue, plant cell, or host cell, respectively, that lacks the herbicide-resistance characteristics and/or particular polynucleotide of the invention that are disclosed herein. The use of the term "wild-type" is not, therefore, intended to imply that a plant, plant 20 tissue, plant cell, or other host cell lacks recombinant DNA in its genome, and/or does not possess herbicide-resistant characteristics that are different from those disclosed herein. As used herein unless clearly indicated otherwise, the term "plant" intended to mean a plant at any developmental stage, as well as any part or parts of a plant that may be attached to or separate from a whole intact plant. Such parts of a plant include, but are 25 not limited to, organs, tissues, and cells of a plant. Examples of particular plant parts include a stem, a leaf, a root, an inflorescence, a flower, a floret, a fruit, a pedicle, a peduncle, a stamen, an anther, a stigma, a style, an ovary, a petal, a sepal, a carpel, a root tip, a root cap, a root hair, a leaf hair, a seed hair, a pollen grain, a microspore, a cotyledon, a hypocotyl, an epicotyl, xylem, phloem, parenchyma, endosperm, a 30 companion cell, a guard cell, and any other known organs, tissues, and cells of a plant. Furthermore, it is recognized that a seed is a plant. The plants of the present invention include both non-transgenic plants and transgenic plants. By "non-transgenic plant" is intended to mean a plant lacking recombinant DNA in its genome. By "transgenic plant" is intended to mean a plant - 18comprising recombinant DNA in its genome. Such a transgenic plant can be produced by introducing recombinant DNA into the genome of the plant. When such recombinant DNA is incorporated into the genome of the transgenic plant, progeny of the plant can also comprise the recombinant DNA. A progeny plant that comprises at least a portion of 5 the recombinant DNA of at least one progenitor transgenic plant is also a transgenic plant. The present invention provides the herbicide-resistant sunflower line that is referred to herein as S4897 and progeny and derivatives thereof that comprise the herbicide-resistance characteristics of S4897. A deposit of seeds of the GM40 sunflower which is derived from sunflower line S4897 and comprises the herbicide-resistance 10 characteristics of S4897 was made with the Patent Depository of the American Type Culture Collection (ATCC), Mansassas, VA 20110 USA on May 17, 2005 and assigned ATCC Patent Deposit Number PTA-6716. The deposit of sunflower line GM40 was made for a term of at least 30 years and at least 5 years after the most recent request for the furnishing of a sample of the deposit is received by the ATCC, Additionally, 15 Applicants have satisfied all the requirements of 37 C.F.R. §§ 1.801-1.809, including providing an indication of the viability of the sample. The present invention further provides the herbicide-resistant sunflower line that is referred to herein as GM1606. A deposit of seeds of the sunflower GM1606 was made with the Patent Depository of the American Type Culture Collection (ATCC), Mansassas, 20 VA 20110 USA on May 19, 2006 and assigned ATCC Patent Deposit Number PTA 7606. The deposit of sunflower GM1606 was made for a term of at least 30 years and at least 5 years after the most recent request for the furnishing of a sample of the deposit is received by the ATCC. Additionally, Applicants have satisfied all the requirements of 37 C.F.R. §§ 1.801-1.809, including providing an indication of the viability of the sample. 25 The present invention provides herbicide-resistant sunflower plants that were produced by mutation breeding. Wild-type sunflower plants were mutagenized by exposing the plants to a mutagen, particularly a chemical mutagen, more particularly ethyl methanesulfonate (EMS). However, the present invention is not limited to herbicide-resistant sunflower plants that are produced by a mutagenesis method involving 30 the chemical mutagen EMS. Any mutagenesis method known in the art may be used to produce the herbicide-resistant sunflower plants of the present invention. Such mutagenesis methods can involve, for example, the use of any one or more of the following mutagens: radiation, such as X-rays, Gamma rays (e.g., cobalt 60 or cesium 137), neutrons, (e.g., product of nuclear fission by uranium 235 in an atomic reactor), -19- Beta radiation (e.g., emitted from radioisotopes such as phosphorus 32 or carbon 14), and ultraviolet radiation (preferably from 2500 to 2900 nm), and chemical mutagens such as base analogues (e.g., 5-bromo-uracil), related compounds (e.g,, 8-ethoxy caffeine), antibiotics (e.g., streptonigrin), alkylating agents (e.g., sulfur mustards, nitrogen mustards, 5 epoxides, ethylenamines, sulfates, sulfonates, sulfones, lactones), azide, hydroxylamine, nitrous acid, or acridines. Herbicide-resistant plants can also be produced by using tissue culture methods to select for plant cells comprising herbicide-resistance mutations and then regenerating herbicide-resistant plants therefrom. See, for example, U.S. Patent Nos. 5,773,702 and 5,859,348, both of which are herein incorporated in their entirety by 10 reference. Further details of mutation breeding can be found in "Principals of Cultivar Development" Fehr, 1993 Macmillan Publishing Company the disclosure of which is incorporated herein by reference. Analysis of the AHIASL1 gene of the sunflower plant of the S4897 and GM1606 lines revealed that the mutation that results in the substitution of a threonine for the 15 alanine that is found at amino acid position 7 in the wild-type AHASL1 amino acid sequence for SEQ ID NO: 4. Amino acid position 7 in SEQ ID NOS: 2 and 4 corresponds to amino acid position 107 in the full-length amino acid sequence of a sunflower AHASLI protein set forth in SEQ ID NO: 12. Thus, the present invention discloses that substituting another amino acid for the alanine at amino acid position 107, 20 or equivalent position, in an AHASL protein can cause a sunflower plant to have enhanced resistance to a herbicide, particularly an imidazolinone and/or sulfonylurea herbicide. As disclosed in Example 6 below, the alanine at amino acid position 107 occurs within a conserved region of AHASL proteins. Similarly, amino acid substitutions in other conserved regions of AHASL proteins have been disclosed that are known to 25 confer herbicide resistance on a plant that comprises such an AHASL protein. Accordingly, the herbicide-resistant sunflower plants of the invention include, but are not limited to those sunflower plants which comprise in their genomes at least one copy of an AHASL polynucleotide that encodes a herbicide-resistant AHASL protein that comprises a threonine at amino acid position 107 or equivalent position. 30 The sunflower plants of the invention further include plants that comprise, relative to the wild-type AHASL protein, a threonine or another amino acid other than alanine at amino acid position 107 or equivalent position, and one or more additional amino acid substitutions in the AHASL protein relative to the wild-type AHASL protein, wherein such a sunflower plant has increased resistance to at least one herbicide when compared - 20 to a wild-type sunflower plant. Such sunflower plants comprise AHASL proteins that comprise a threonine or another amino acid other than alanine at amino acid position 107 or equivalent position and at least one member selected from the group consisting of: an alanine, threonine, histidine, leucine, arginine, isoleucine, glutamine, or serine at amino 5 acid position 182 or equivalent position; an isoleucine or an amino acid other than threonine at amino acid position 188 or equivalent position; an aspartate or valine at amino acid position 190 or equivalent position; a leucine at amino acid position 559 or equivalent position; and an asparagine, threonine, phenylalanine, or valine at amino acid position 638 or equivalent position. 10 The present invention provides AHASL proteins with amino acid substitutions at particular amino acid positions within conserved regions of the sunflower AHASL proteins disclosed herein. Furthermore, those of ordinary skill will recognize that such amino acid positions can vary depending on whether amino acids are added or removed from, for example, the N-terminal end of an amino acid sequence. Thus, the invention 15 encompasses the amino acid substitutions at the recited position or equivalent position (e.g., "amino acid position 107 or equivalent position"). By "equivalent position" is intended to mean a position that is within the same conserved region as the exemplified amino acid position. Such conserved regions are know in the art (see Table 4 below) or can be determined by multiple sequence alignments as disclosed herein or by methods 20 known in the art. In addition, the present invention provides AHASL polypeptides comprising amino acid substitutions that are known to confer resistance on a plant to at least one herbicide, particularly an imidazolinone herbicide and/or a sulfonylurea herbicide. Such AHASL polypeptides include, for example, those that comprise a threonine at amino acid 25 position 107 and at least one member selected from the group consisting of: an alanine, threonine, histidine, leucine, arginine, isoleucine, glutamine, or serine at amino acid position 182 or equivalent position; an isoleucine or another amino acid other than threonine at amino acid position 188 or equivalent position; an aspartate or valine at amino acid position 190 or equivalent position; an aspartate or valine at amino acid 30 position 190 or equivalent position; a leucine at amino acid position 559 or equivalent position; and an asparagine, threonine, phenylalanine, or valine at amino acid position 638 or equivalent position. The invention further provides isolated polynucleotides encoding such AHASL polypeptides, as well as expression cassettes, transformation - 21 vectors, transformed host cells, transformed plants, and methods comprising such polynucleotides. The present invention provides methods for enhancing the tolerance or resistance of a plant, plant tissue, plant cell, or other host cell to at least one herbicide that interferes 5 with the activity of the AHAS enzyme. Preferably, such a herbicide is an imidazolinone herbicide, a sulfonylurea herbicide, a triazolopyrimidine herbicide, a pyrimidinyloxybenzoate herbicide, a sulfonylamino-carbonyltriazolinone herbicide, or mixture thereof. More preferably, such a herbicide is an imidazolinone herbicide, a sulfonylurea herbicide, or mixture thereof. For the present invention, the imidazolinone 10 herbicides include, but are not limited to, PURSUIT® (imazethapyr), CADRE® (imazapic), RAPTOR@ (imazamox), SCEPTER® (imazaquin), ASSERT® (imazethabenz), ARSENAL@ (imazapyr), a derivative of any of the aforementioned herbicides, and a mixture of two or more of the aforementioned herbicides, for example, imazapyr/imazamox (ODYSSEY®). More specifically, the imidazolinone herbicide can 15 be selected from, but is not limited to, 2- (4-isopropyl-4-methyl-5-oxo-2-imidiazolin-2-yl) -nicotinic acid, [2- (4-isopropyl)-4-} [methyl-5-oxo-2-imidazolin-2-yl)-3 quinolinecarboxylic] acid, [5-ethyl-2- (4-isopropyl-] 4-methyl-5-oxo-2-imidazolin-2-yl) nicotinic acid, 2- (4-isopropyl-4-methyl-5-oxo-2- imidazolin-2-yl)-5- (methoxymethyl) nicotinic acid, [2- (4-isopropyl-4-methyl-5-oxo-2-J imidazolin-2-yl)-5-methylnicotinic 20 acid, and a mixture of methyl [6- (4-isopropyl-4-] methyl-5-oxo-2-imidazolin-2-yl) -m toluate and methyl [2- (4-isopropyl-4-methyl-5-] oxo-2-imidazolin-2-yl) -p-toluate. The use of 5-ethyl-2- (4-isopropyl-4-methyl-5-oxo- 2-imidazolin-2-yl) -nicotinic acid and [2 (4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-] yl)-5- (methoxymethyl)-nicotinic acid is preferred. The use of [2- (4-isopropyl-4-] methyl-5-oxo-2-imidazolin-2-yl)-5 25 (methoxymethyl)-nicotinic acid is particularly preferred. For the present invention, the sulfonylurea herbicides include, but are not limited to, chlorsulfuron, metsulfuron methyl, sulfometuron methyl, chlorimuron ethyl, thifensulfuron methyl, tribenuron methyl, bensulfuron methyl, nicosulfuron, ethametsulfuron methyl, rimsulfuron, triflusulfuron methyl, triasulfuron, primisulfuron 30 methyl, cinosulfuron, amidosulfluon, fluzasulfuron, imazosulfuron, pyrazosulfuron ethyl, halosulfuron, azimsulfuron, cyclosulfuron, ethoxysulfuron, flazasulfuron, flupyrsulfuron methyl, foramsulfuron, iodosulfuron, oxasulfuron, mesosulfuron, prosulfuron, sulfosulfuron, trifloxysulfuron, tritosulfuron, a derivative of any of the aforementioned herbicides, and a mixture of two or more of the aforementioned herbicides. The -22triazolopyrimidine herbicides of the invention include, but are not limited to, cloransulam, diclosulam, florasulam, flumetsulam, metosulam, and penoxsulam. The pyrimidinyloxybenzoate herbicides of the invention include, but are not limited to, bispyribac, pyrithiobac, pyriminobac, pyribenzoxim and pyriftalid. The sulfonylamino 5 carbonyltriazolinone herbicides include, but are not limited to, flucarbazone and propoxycarbazone. It is recognized that pyrimidinyloxybenzoate herbicides are closely related to the pyrimidinylthiobenzoate herbicides and are generalized under the heading of the latter name by the Weed Science Society of America. Accordingly, the herbicides of the 10 present invention further include pyrimidinylthiobenzoate herbicides, including, but not limited to, the pyrimidinyloxybenzoate herbicides described above. The present invention provides methods for enhancing AHAS activity in a plant comprising transforming a plant with a polynucleotide construct comprising a promoter operably linked to an AHASLI nucleotide sequence of the invention. The methods 15 involve introducing a polynucleotide construct of the invention into at least one plant cell and regenerating a transformed plant therefrom. The methods involve the use of a promoter that is capable of driving gene expression in a plant cell. Preferably, such a promoter is a constitutive promoter or a tissue-preferred promoter. The methods find use in enhancing or increasing the resistance of a plant to at least one herbicide that interferes 20 with the catalytic activity of the AHAS enzyme, particularly an imidazolinone herbicide. The present invention provides expression cassettes for expressing the polynucleotides of the invention in plants, plant tissues, plant cells, and other host cells. The expression cassettes comprise a promoter expressible in the plant, plant tissue, plant cell, or other host cells of interest operably linked to a polynucleotide of the invention that 25 comprises a nucleotide sequence encoding either a full-length (i.e. including the chloroplast transit peptide) or mature AHASLI protein (i.e. without the chloroplast transit peptide). If expression is desired in the plastids or chloroplasts of plants or plant cells, the expression cassette may also comprise an operably linked chloroplast-targeting sequence that encodes a chloroplast transit peptide. 30 The expression cassettes of the invention find use in a method for enhancing the herbicide tolerance of a plant or a host cell. The method involves transforming the plant or host cell with an expression cassette of the invention, wherein the expression cassette comprises a promoter that is expressible in the plant or host cell of interest and the promoter is operably linked to a polynucleotide of the invention that comprises a - 23 nucleotide sequence encoding an imidazolinone-resistant AHASL protein of the invention. The use of the term "polynucleotide constructs" herein is not intended to limit the present invention to polynucleotide constructs comprising DNA. Those of ordinary skill 5 in the art will recognize that polynucleotide constructs, particularly polynucleotides and oligonucleotides, comprised of ribonucleotides and combinations of ribonucleotides and deoxyribonucleotides may also be employed in the methods disclosed herein. Thus, the polynucleotide constructs of the present invention encompass all polynucleotide constructs that can be employed in the methods of the present invention for transforming 10 plants including, but not limited to, those comprised of deoxyribonucleotides, ribonucleotides, and combinations thereof. Such deoxyribonucleotides and ribonucleotides include both naturally occurring molecules and synthetic analogues. The polynucleotide constructs of the invention also encompass all forms of polynucleotide constructs including, but not limited to, single-stranded forms, double-stranded forms, 15 hairpins, stem-and-loop structures, and the like. Furthermore, it is understood by those of ordinary skill in the art that each nucleotide sequences disclosed herein also encompasses the complement of that exemplified nucleotide sequence, Furthermore, it is recognized that the methods of the invention may employ a polynucleotide construct that is capable of directing, in a transformed plant, the 20 expression of at least one protein, or at least one RNA, such as, for example, an antisense RNA that is complementary to at least a portion of an mRNA. Typically such a polynucleotide construct is comprised of a coding sequence for a protein or an RNA operably linked to 5' and 3' transcriptional regulatory regions. Alternatively, it is also recognized that the methods of the invention may employ a polynucleotide construct that 25 is not capable of directing, in a transformed plant, the expression of a protein or an RNA. Further, it is recognized that, for expression of a polynucleotide of the invention in a host cell of interest, the polynucleotide is typically operably linked to a promoter that is capable of driving gene expression in the host cell of interest. The methods of the invention for expressing the polynucleotides in host cells do not depend on particular 30 promoter. The methods encompass the use of any promoter that is known in the art and that is capable of driving gene expression in the host cell of interest. The present invention encompasses AHASL polynucleotide molecules and fragments and variants thereof. Polynucleotide molecules that are fragments of these nucleotide sequences are also encompassed by the present invention. By "fragment" is - 24 intended a portion of the nucleotide sequence encoding an AHASL protein of the invention. A fragment of an AHASL nucleotide sequence of the invention may encode a biologically active portion of an AHASL protein, or it may be a fragment that can be used as a hybridization probe or PCR primer using methods disclosed below. A biologically 5 active portion of an AHASL protein can be prepared by isolating a portion of one of the AHASL nucleotide sequences of the invention, expressing the encoded portion of the AHASL protein (e.g., by recombinant expression in vitro), and assessing the activity of the encoded portion of the AHASLI protein. Polynucleotide molecules that are fragments of an AHASL nucleotide sequence comprise at least about 15, 20, 50, 75, 100, 10 200, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, or 1100 nucleotides, or up to the number of nucleotides present in a full-length nucleotide sequence disclosed herein (for example, 1178 nucleotides for both SEQ ID NOS: 1 and 3) depending upon the intended use. A fragment of an AHASL nucleotide sequence that encodes a biologically active 15 portion of an AHASL protein of the invention will encode at least about 15, 25, 30, 50, 75, 100, 125, 150, 175, 200, 250, 300, or 350 contiguous amino acids, or up to the total number of amino acids present in a full-length AHASL1 protein of the invention (for example, 392 amino acids for both SEQ ID NOS: 2 and 4). Fragments of an AHASLI nucleotide sequence that are useful as hybridization probes for PCR primers generally 20 need not encode a biologically active portion of an AHASLI protein. Polynucleotide molecules that are variants of the nucleotide sequences disclosed herein are also encompassed by the present invention. "Variants" of the AHASL nucleotide sequences of the invention include those sequences that encode the AHASL proteins disclosed herein but that differ conservatively because of the degeneracy of the 25 genetic code. These naturally occurring allelic variants can be identified with the use of well-known molecular biology techniques, such as polymerase chain reaction (PCR) and hybridization techniques as outlined below. Variant nucleotide sequences also include synthetically derived nucleotide sequences that have been generated, for example, by using site-directed mutagenesis but which still encode the AHASL1 protein disclosed in 30 the present invention as discussed below, Generally, nucleotide sequence variants of the invention will have at least about 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to a particular nucleotide sequence disclosed herein. A variant AHASL nucleotide sequence will encode an AHASL protein, respectively, that has an amino acid sequence having at least about 70%, 75%, 80%, 85%, -25 - 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to the amino acid sequence of an AHASL protein disclosed herein. In addition, the skilled artisan will further appreciate that changes can be introduced by mutation into the nucleotide sequences of the invention thereby leading to 5 changes in the amino acid sequence of the encoded AHASL proteins without altering the biological activity of the AHASL proteins. Thus, an isolated polynucleotide molecule encoding an AHASL protein having a sequence that differs from that of SEQ ID NOS: 1 or 3, respectively, can be created by introducing one or more nucleotide substitutions, additions, or deletions into the corresponding nucleotide sequence disclosed herein, such 10 that one or more amino acid substitutions, additions or deletions are introduced into the encoded protein. Mutations can be introduced by standard techniques, such as site directed mutagenesis and PCR-mediated mutagenesis. Such variant nucleotide sequences are also encompassed by the present invention. For example, preferably, conservative amino acid substitutions may be made at 15 one or more predicted, preferably nonessential amino acid residues. A "nonessential" amino acid residue is a residue that can be altered from the wild-type sequence of an AHASL protein (e.g., the sequence of SEQ ID NOS: 2 and 4, respectively) without altering the biological activity, whereas an "essential" amino acid residue is required for biological activity. A "conservative amino acid substitution" is one in which the amino 20 acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains 25 (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). Such substitutions would not be made for conserved amino acid residues, or for amino acid residues residing within a conserved motif. 30 The proteins of the invention may be altered in various ways including amino acid substitutions, deletions, truncations, and insertions. Methods for such manipulations are generally known in the art. For example, amino acid sequence variants of the AHASL proteins can be prepared by mutations in the DNA. Methods for mutagenesis and nucleotide sequence alterations are well known in the art. See, for example, Kunkel -26- (1985) Proc. Nati. Acad Sci. USA 82:488-492; Kunkel et al. (1987)Methods in Enzyiol. 154:367-382; U.S. Patent No. 4,873,192; Walker and Gaastra, eds. (1983) Techniques in Molecular Biology (MacMillan Publishing Company, New York) and the references cited therein. Guidance as to appropriate amino acid substitutions that do not affect biological 5 activity of the protein of interest may be found in the model of Dayhoff et al. (1978) Atlas ofProtein Sequence and Structure (Natl. Biomed. Res. Found., Washington, D.C.), herein incorporated by reference. Conservative substitutions, such as exchanging one amino acid with another having similar properties, may be preferable. Alternatively, variant AHASL nucleotide sequences can be made by introducing 10 mutations randomly along all or part of an AHASL coding sequence, such as by saturation mutagenesis, and the resultant mutants can be screened for AHAS activity to identify mutants that retain AHAS activity, including herbicide-resistant AHAS activity. Following mutagenesis, the encoded protein can be expressed recombinantly, and the activity of the protein can be determined using standard assay techniques. 15 Thus, the nucleotide sequences of the invention include the sequences disclosed herein as well as fragments and variants thereof. The AHASL nucleotide sequences of the invention, and fragments and variants thereof, can be used as probes and/or primers to identify and/or clone AHASL homologues in other plants. Such probes can be used to detect transcripts or genomic sequences encoding the same or identical proteins, 20 In this manner, methods such as PCR, hybridization, and the like can be used to identify such sequences having substantial identity to the sequences of the invention. See, for example, Sambrook et al. (1989)Molecular Cloning: Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, NY) and Innis, et al. (1990) PCR Protocols: A Guide to Methods and Applications (Academic Press, NY). AHASL 25 nucleotide sequences isolated based on their sequence identity to the AHASLI nucleotide sequences set forth herein or to fragments and variants thereof are encompassed by the present invention. In a hybridization method, all or part of a known AHASL nucleotide sequence can be used to screen cDNA or genomic libraries. Methods for construction of such cDNA 30 and genomic libraries are generally known in the art and are disclosed in Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, NY). The so-called hybridization probes may be genomic DNA fragments, cDNA fragments, RNA fragments, or other oligonucleotides, and may be labeled with a detectable group such as 32 P, or any other detectable marker, such as other -27radioisotopes, a fluorescent compound, an enzyme, or an enzyme co-factor. Probes for hybridization can be made by labeling synthetic oligonucleotides based on the known AHASL nucleotide sequence disclosed herein. Degenerate primers designed on the basis of conserved nucleotides or amino acid residues in a known AHASL nucleotide sequence 5 or encoded amino acid sequence can additionally be used. The probe typically comprises a region of nucleotide sequence that hybridizes under stringent conditions to at least about 12, preferably about 25, more preferably about 50, 75, 100, 125, 150, 175, 200, 250, 300, 350, 400, 500, 600, 700, 800, 900, 1000, 1100, or 1178 consecutive nucleotides of an AHASL nucleotide sequence of the invention or a fragment or variant thereof. Preparation 10 of probes for hybridization is generally known in the art and is disclosed in Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, New York), herein incorporated by reference. For example, the entire AHASL sequence disclosed herein, or one or more portions thereof, may be used as a probe capable of specifically hybridizing to corresponding 15 AHASL sequences and messenger RNAs. Hybridization techniques include hybridization screening of plated DNA libraries (either plaques or colonies; see, for example, Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, New York). Hybridization of such sequences may be carried out under stringent conditions. 20 By "stringent conditions" or "stringent hybridization conditions" is intended conditions under which a probe will hybridize to its target sequence to a detectably greater degree than to other sequences (e.g., at least 2-fold over background). Stringent conditions are sequence-dependent and will be different in different circumstances. Typically, stringent conditions will be those in which the salt concentration is less 25 than about 1.5 M Na ion, typically about 0.01 to 1.0 M Na ion concentration (or other salts) at pH 7.0 to 8.3 and the temperature is at least about 30*C for short probes (e.g., 10 to 50 nucleotides) and at least about 60*C for long probes (e.g., greater than 50 nucleotides). Stringent conditions may also be achieved with the addition of destabilizing agents such as formamide. Exemplary low stringency conditions include hybridization 30 with a buffer solution of 30 to 35% formamide, 1 M NaCl, 1% SDS (sodium dodecyl sulphate) at 37*C, and awash in IX to 2X SSC (20X SSC = 3.0 M NaClI/0.3 M trisodium citrate) at 50 to 55 0 C. Exemplary moderate stringency conditions include hybridization in 40 to 45% formamide, 1.0 M NaCl, 1% SDS at 37'C, and a wash in 0.5X to IX SSC at 55 to 60*C. Exemplary high stringency conditions include hybridization in 50% - 28 formamide, 1 M NaCl, 1% SDS at 37*C, and a wash in 0. IX SSC at 60 to 65*C. Optionally, wash buffers may comprise about 0.1% to about 1% SDS. The duration of hybridization is generally less than about 24 hours, usually about 4 to about 12 hours, Specificity is typically the function of post-hybridization washes, the critical 5 factors being the ionic strength and temperature of the final wash solution. For DNA DNA hybrids, the Tm can be approximated from the equation of Meinkoth and Wahl (1984) Anal. Biochem. 138:267-284: Tm = 81.5*C + 16.6 (log M) + 0.41 (%GC) - 0.61 (% form) - 500/L; where M is the molarity of monovalent cations, %GC is the percentage of guanosine and cytosine nucleotides in the DNA, % form is the percentage of 10 formamide in the hybridization solution, and L is the length of the hybrid in base pairs. The Tm is the temperature (under defined ionic strength and pH) at which 50% of a complementary target sequence hybridizes to a perfectly matched probe. Tm is reduced by about 1*C for each 1% of mismatching; thus, Tm, hybridization, and/or wash conditions can be adjusted to hybridize to sequences of the desired identity. For example, 15 if sequences with >90% identity are sought, the Tm can be decreased 10*C. Generally, stringent conditions are selected to be about 5*C lower than the thermal melting point (Tm) for the specific sequence and its complement at a defined ionic strength and pH. However, severely stringent conditions can utilize a hybridization and/or wash at 1, 2, 3, or 4C lower than the thermal melting point (Tm); moderately stringent conditions can 20 utilize a hybridization and/or wash at 6, 7, 8, 9, or 1 0C lower than the thermal melting point (Tm); low stringency conditions can utilize a hybridization and/or wash at 11, 12, 13, 14, 15, or 20*C lower than the thermal melting point (Tm). Using the equation, hybridization and wash compositions, and desired Tm, those of ordinary skill will understand that variations in the stringency of hybridization and/or wash solutions are 25 inherently described. If the desired degree of mismatching results in a Tm of less than 45*C (aqueous solution) or 32*C (formamide solution), it is preferred to increase the SSC concentration so that a higher temperature can be used. An extensive guide to the hybridization of nucleic acids is found in Tijssen (1993) Laboratory Techniques in Biochemistry and Molecular Biology-Hybridization with Nucleic Acid Probes, Part I, 30 Chapter 2 (Elsevier, New York); and Ausubel et al., eds. (1995) Current Protocols in Molecular Biology, Chapter 2 (Greene Publishing and Wiley-Interscience, New York). See Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual(2d ed., Cold Spring Harbor Laboratory Press, Plainview, New York). - 29- It is recognized that the polynucleotide molecules and proteins of the invention encompass polynucleotide molecules and proteins comprising a nucleotide or an amino acid sequence that is sufficiently identical to the nucleotide sequence of SEQ ID NOS: 1 and/or 3, or to the amino acid sequence of SEQ ID NOS: 2 and/or 4. The term 5 "sufficiently identical" is used herein to refer to a first amino acid or nucleotide sequence that contains a sufficient or minimum number of identical or equivalent (e.g., with a similar side chain) amino acid residues or nucleotides to a second amino acid or nucleotide sequence such that the first and second amino acid or nucleotide sequences have a common structural domain and/or common functional activity. For example, 10 amino acid or nucleotide sequences that contain a common structural domain having at least about 45%, 55%, or 65% identity, preferably 75% identity, more preferably 85%, 95%, or 98% identity are defined herein as sufficiently identical. To determine the percent identity of two amino acid sequences or of two nucleic acids, the sequences are aligned for optimal comparison purposes. The percent identity 15 between the two sequences is a function of the number of identical positions shared by the sequences (i.e., percent identity = number of identical positions/total number of positions (e.g., overlapping positions) x 100). In one embodiment, the two sequences are the same length. The percent identity between two sequences can be determined using techniques similar to those described below, with or without allowing gaps. In 20 calculating percent identity, typically exact matches are counted. The determination of percent identity between two sequences can be accomplished using a mathematical algorithm. A preferred, nonlimiting example of a mathematical algorithm utilized for the comparison of two sequences is the algorithm of Karlin and Altschul (1990) Proc. Nati. Acad Sci. USA 87:2264, modified as in Karlin and 25 Altschul (1993) Proc. Natl. Acad Sci. USA 90:5873-5877. Such an algorithm is incorporated into the NBLAST and XBLAST programs of Altschul et al. (1990) J. Mol. Biol. 215:403. BLAST nucleotide searches can be performed with the NBLAST program, score = 100, wordlength = 12, to obtain nucleotide sequences homologous to the polynucleotide molecules of the invention. BLAST protein searches can be performed 30 with the XBLAST program, score = 50, wordlength = 3, to obtain amino acid sequences homologous to protein molecules of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al. (1997) Nucleic Acids Res. 25:3389. Alternatively, PSI-Blast can be used to perform an iterated search that detects distant relationships between molecules. See Altschul et al. -30- (1997) supra. When utilizing BLAST, Gapped BLAST, and PSI-Blast programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used, See http://www.ncbi.nlm.nih.gov. Another preferred, non-limiting example of a mathematical algorithm utilized for the comparison of sequences is the algorithm of 5 Myers and Miller (1988) CABIOS 4:11-17. Such an algorithm is incorporated into the ALIGN program (version 2.0), which is part of the GCG sequence alignment software package. When utilizing the ALIGN program for comparing amino acid sequences, a PAM120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used. Alignment may also be performed manually by inspection. 10 Unless otherwise stated, sequence identity/similarity values provided herein refer to the value obtained using the full-length sequences of the invention and using multiple alignment by mean of the algorithm Clustal W (Nucleic Acid Research, 22(22):4673 4680, 1994) using the program AlignX included in the software package Vector NTI Suite Version 7 (InforMax, Inc., Bethesda, MD, USA) using the default parameters; or 15 any equivalent program thereof. By "equivalent program" is intended any sequence comparison program that, for any two sequences in question, generates an alignment having identical nucleotide or amino acid residue matches and an identical percent sequence identity when compared to the corresponding alignment generated by AlignX in the software package Vector NTI Suite Version 7. 20 The AHASL nucleotide sequences of the invention include both the naturally occurring sequences as well as mutant forms, particularly mutant forms that encode AHASL proteins comprising herbicide-resistant AHAS activity. Likewise, the proteins of the invention encompass both naturally occurring proteins as well as variations and modified forms thereof. Such variants will continue to possess the desired AHAS 25 activity. Obviously, the mutations that will be made in the DNA encoding the variant must not place the sequence out of reading frame and preferably will not create complementary regions that could produce secondary mRNA structure. See, EP Patent Application Publication No. 75,444. The deletions, insertions, and substitutions of the protein sequences encompassed 30 herein are not expected to produce radical changes in the characteristics of the protein. However, when it is difficult to predict the exact effect of the substitution, deletion, or insertion in advance of doing so, one skilled in the art will appreciate that the effect will be evaluated by routine screening assays. That is, the activity can be evaluated by AHAS -31activity assays. See, for example, Singh et al. (1988) Anal. Biochem. 171:173-179, herein incorporated by reference. Variant nucleotide sequences and proteins also encompass sequences and proteins derived from a mutagenic and recombinogenic procedure such as DNA shuffling. With 5 such a procedure, one or more different AHASL coding sequences can be manipulated to create a new AHASL protein possessing the desired properties. In this manner, libraries of recombinant polynucleotides are generated from a population of related sequence polynucleotides comprising sequence regions that have substantial sequence identity and can be homologously recombined in vitro or in vivo. For example, using this approach, 10 sequence motifs encoding a domain of interest may be shuffled between the AHASL gene of the invention and other known AHASL genes to obtain a new gene coding for a protein with an improved property of interest, such as an increased Km in the case of an enzyme. Strategies for such DNA shuffling are known in the art. See, for example, Stemmer (1994) Proc. Natl. Acad Sci. USA 91:10747-10751; Stemmer (1994) Nature 370:389 15 391; Crameri et al. (1997) Nature Biotech. 15:436-438; Moore et al. (1997) J. Mol. Biol. 272:336-347; Zhang et al. (1997) Proc. Natl. Acad Sci. USA 94:4504-4509; Crameri et al. (1998) Nature 391:288-291; and U.S. Patent Nos. 5,605,793 and 5,837,458. The nucleotide sequences of the invention can be used to isolate corresponding sequences from other organisms, particularly other plants, more particularly other dicots. 20 In this manner, methods such as PCR, hybridization, and the like can be used to identify such sequences based on their sequence homology to the sequences set forth herein. Sequences isolated based on their sequence identity to the entire AHASL polynucleotide sequences set forth herein or to fragments thereof are encompassed by the present invention. Thus, isolated polynucleotide sequences that encode for an AHASL protein 25 and which hybridize under stringent conditions to the sequence disclosed herein, or to fragments thereof, are encompassed by the present invention. In a PCR approach, oligonucleotide primers can be designed for use in PCR reactions to amplify corresponding DNA sequences from cDNA or genomic DNA extracted from any plant of interest. Methods for designing PCR primers and PCR 30 cloning are generally known in the art and are disclosed in Sambrook et al. (1989) Molecular Cloning: A Laboratoy Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, New York). See also Innis et al., eds. (1990) PCR Protocols: A Guide to Methods andApplications (Academic Press, New York); Innis and Gelfand, eds. (1995) PCR Strategies (Academic Press, New York); and Innis and Gelfand, eds, (1999) PCR -32- Methods Manual (Academic Press, New York). Known methods of PCR include, but are not limited to, methods using paired primers, nested primers, single specific primers, degenerate primers, gene-specific primers, vector-specific primers, partially-mismatched primers, and the like. 5 The AHASL polynucleotide sequences of the invention are provided in expression cassettes for expression in the plant of interest. The cassette will include 5' and 3' regulatory sequences operably linked to an AHASL polynucleotide sequence of the invention. By "operably linked" is intended a functional linkage between a promoter and a second sequence, wherein the promoter sequence initiates and mediates transcription of 10 the DNA sequence corresponding to the second sequence, Generally, operably linked means that the nucleic acid sequences being linked are contiguous and, where necessary to join two protein coding regions, contiguous and in the same reading frame. The cassette may additionally contain at least one additional gene to be cotransformed into the organism. Alternatively, the additional gene(s) can be provided on multiple expression 15 cassettes. Such an expression cassette is provided with a plurality of restriction sites for insertion of the AHASL polynucleotide sequence to be under the transcriptional regulation of the regulatory regions. The expression cassette may additionally contain selectable marker genes. 20 The expression cassette will include in the 5'-3' direction of transcription, a transcriptional and translational initiation region (i.e., a promoter), an ANASL polynucleotide sequence of the invention, and a transcriptional and translational termination region (i.e., termination region) functional in plants. The promoter may be native or analogous, or foreign or heterologous, to the plant host and/or to the AHASL 25 polynucleotide sequence of the invention. Additionally, the promoter may be the natural sequence or alternatively a synthetic sequence. Where the promoter is "foreign" or "heterologous" to the plant host, it is intended that the promoter is not found in the native plant into which the promoter is introduced Where the promoter is "foreign" or "heterologous" to the AHASL polynucleotide sequence of the invention, it is intended that 30 the promoter is not the native or naturally occurring promoter for the operably linked AHASL polynucleotide sequence of the invention. As used herein, a chimeric gene comprises a coding sequence operably linked to a transcription initiation region that is heterologous to the coding sequence. - 33 - While it may be preferable to express the AHASL polynucleotides of the invention using heterologous promoters, the native promoter sequences may be used. Such constructs would change expression levels of the AHASL protein in the plant or plant cell. Thus, the phenotype of the plant or plant cell is altered. 5 The termination region may be native with the transcriptional initiation region, may be native with the operably linked AHASL sequence of interest, may be native with the plant host, or may be derived from another source (i.e., foreign or heterologous to the promoter, the AHASL polynucleotide sequence of interest, the plant host, or any combination thereof) Convenient termination regions are available from the Ti-plasmid 10 of A. tuniefaciens, such as the octopine synthase and nopaline synthase termination regions. See also Guerineau et al. (1991)Mol. Gen. Genet. 262:141-144; Proudfoot (1991) Cell 64:671-674; Sanfacon et al. (1991) Genes Dev 5:141-149; Mogen et al. (1990) Plant Cell2:1261-1272; Munroe et al. (1990) Gene 91:151-158; Ballas et al. (1989) Nucleic Acids Res. 17:7891-7903; and Joshi et al. (1987) Nucleic Acid Res. 15 15:9627-9639. Where appropriate, the gene(s) may be optimized for increased expression in the transformed plant. That is, the genes can be synthesized using plant-preferred codons for improved expression. See, for example, Campbell and Gowri (1990) Plant Physiol. 92:1 11 for a discussion of host-preferred codon usage. Methods are available in the art for 20 synthesizing plant-preferred genes. See, for example, U.S. Patent Nos. 5,380,831, and 5,436,391, and Murray et al. (1989) Nucleic Acids Res. 17:477-498, herein incorporated by reference. Additional sequence modifications are known to enhance gene expression in a cellular host. These include elimination of sequences encoding spurious polyadenylation 25 signals, exon-intron splice site signals, transposon-like repeats, and other such well characterized sequences that may be deleterious to gene expression. The G-C content of the sequence may be adjusted to levels average for a given cellular host, as calculated by reference to known genes expressed in the host cell. When possible, the sequence is modified to avoid predicted hairpin secondary mRNA structures. 30 Nucleotide sequences for enhancing gene expression can also be used in the plant expression vectors. These include the introns of the maize AdhI, intronl gene (Callis et al. Genes and Development 1:1183-1200, 1987), and leader sequences, (W-sequence) from the Tobacco Mosaic virus (TMV), Maize Chlorotic Mottle Virus and Alfalfa Mosaic Virus (Gallie et al. Nucleic AcidRes. 15:8693-8711, 1987 and Skuzeski et al. Plant Mo. - 34 - Biol. 15:65-79, 1990). The first intron from the shrunken-1 locus of maize, has been shown to increase expression of genes in chimeric gene constructs. US. Pat. Nos. 5,424,412 and 5,593,874 disclose the use of specific introns in gene expression constructs, and Gallie et al. (Plant Physiol. 106:929-939, 1994) also have shown that 5 introns are useful for regulating gene expression on a tissue specific basis. To further enhance or to optimize AHAS large subunit gene expression, the plant expression vectors of the invention may also contain DNA sequences containing matrix attachment regions (MARs). Plant cells transformed with such modified expression systems, then, may exhibit overexpression or constitutive expression of a nucleotide sequence of the 10 invention. The expression cassettes may additionally contain 5'leader sequences in the expression cassette construct. Such leader sequences can act to enhance translation. Translation leaders are known in the art and include: picornavirus leaders, for example, EMCV leader (Encephalomyocarditis 5' noncoding region) (Elroy-Stein et al. (1989) 15 Proc. Natl. Acad. Sci. USA 86:6126-6130); potyvirus leaders, for example, TEV leader (Tobacco Etch Virus) (Gallie et al. (1995) Gene 165(2):233-238), MDMV leader (Maize Dwarf Mosaic Virus) (Virology 154:9-20), and human immunoglobulin heavy-chain binding protein (BiP) (Macejak et al. (1991) Nature 353:90-94); untranslated leader from the coat protein mRNA of alfalfa mosaic virus (AMV RNA 4) (Jobling et al. (1987) 20 Nature 325:622-625); tobacco mosaic virus leader (TMV) (Gallie et al. (1989) in Molecular Biology ofRNA, ed. Cech (Liss, New York), pp. 237-256); and maize chlorotic mottle virus leader (MCMV) (Lommel et al. (1991) Virology 81:382-385). See also, Della-Cioppa et al. (1987) Plant Physiol. 84:965-968. Other methods known to enhance translation can also be utilized, for example, introns, and the like. 25 In preparing the expression cassette, the various DNA fragments may be manipulated, so as to provide for the DNA sequences in the proper orientation and, as appropriate, in the proper reading frame. Toward this end, adapters or linkers may be employed to join the DNA fragments or other manipulations may be involved to provide for convenient restriction sites, removal of superfluous DNA, removal of restriction sites, 30 or the like. For this purpose, in vitro mutagenesis, primer repair, restriction, annealing, resubstitutions, e.g., transitions and transversions, may be involved. A number of promoters can be used in the practice of the invention, The promoters can be selected based on the desired outcome. The nucleic acids can be combined with constitutive, tissue-preferred, or other promoters for expression in plants. - 35 - Such constitutive promoters include, for example, the core promoter of the Rsyn7 promoter and other constitutive promoters disclosed in WO 99/43838 and U.S. Patent No. 6,072,050; the core CaMV 35S promoter (Odell et al. (1985) Nature 313:810-812); rice actin (McElroy et al. (1990) Plant Cell 2:163-171); ubiquitin (Christensen et al. (1989) 5 Plant Mol. Biol. 12:619-632 and Christensen et al. (1992) PlantMol. Biol 18:675-689); pEMU (Last et al. (1991) Theor. Apple. Genet. 81:581-588); MAS (Velten et al. (1984) EMBO J. 3:2723-2730); ALS promoter (U.S. Patent No. 5,659,026), and the like. Other constitutive promoters include, for example, U.S. Patent Nos. 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; 5,608,142; and 6,177,611. 10 Tissue-preferred promoters can be utilized to target enhanced AHASL1 expression within a particular plant tissue. Such tissue-preferred promoters include, but are not limited to, leaf-preferred promoters, root-preferred promoters, seed-preferred promoters, and stem-preferred promoters. Tissue-preferred promoters include Yamamoto et al. (1997) Plant J. 12(2):255-265; Kawamata et al. (1997) Plant Cell Physiol 15 38(7):792-803; Hansen et al. (1997)Mol. Gen Genet. 254(3):337-343; Russell et al. (1997) Transgenic Res. 6(2):157-168; Rinehart et al. (1996) Plant Physiol. 112(3): 1331 1341; Van Camp et al (1996) PlantPhysiol. 112(2):525-535; Canevascini et al. (1996) Plant PhysioL. 112(2):513-524; Yamamoto et al (1994) Plant Cell Physiol. 35(5):773 778; Lam (1994) Results Prob. Cell Differ. 20:181-196; Orozco et al. (1993) Plant Mol 20 Biol. 23(6):1129-1138; Matsuoka et al. (1993) Proc Natl. Acad Sci. USA 90(20):9586 9590; and Guevara-Garcia et al. (1993) PlantJ 4(3):495-505. Such promoters can be modified, if necessary, for weak expression. In one embodiment, the nucleic acids of interest are targeted to the chloroplast for expression. In this manner, where the nucleic acid of interest is not directly inserted into 25 the chloroplast, the expression cassette will additionally contain a chloroplast-targeting sequence comprising a nucleotide sequence that encodes a chloroplast transit peptide to direct the gene product of interest to the chloroplasts. Such transit peptides are known in the art. With respect to chloroplast-targeting sequences, "operably linked" means that the nucleic acid sequence encoding a transit peptide (i.e., the chloroplast-targeting sequence) 30 is linked to the AHASL polynucleotide of the invention such that the two sequences are contiguous and in the same reading frame. See, for example, Von Heijne et al. (1991) Plant Mol. Biol. Rep. 9:104-126; Clark et al, (1989) J. Biol. Chem. 264:17544-17550; Della-Cioppa et al. (1987) Plant Physiol. 84:965-968; Romer et al. (1993) Biochem. Biophys. Res. Coinmun. 196:1414-1421; and Shah et al. (1986) Science 233:478-48 1. -36- While the AHASL proteins of the invention include a native chloroplast transit peptide, any chloroplast transit peptide known in the art can be fused to the amino acid sequence of a mature AHASL protein of the invention by operably linking a choloroplast-targeting sequence to the 5'-end of a nucleotide sequence encoding a mature AHASL protein of the 5 invention. Chloroplast targeting sequences are known in the art and include the chloroplast small subunit of ribulose-1,5-bisphosphate carboxylase (Rubisco) (de Castro Silva Filho et al. (1996) Plant Mol. Biol. 30:769-780; Schnell et al. (1991) J. Biol. Chem. 266(5):3335-3342); 5-(enolpyruvyl)shikimate-3 -phosphate synthase (EPSPS) (Archer et 10 al. (1990) J Bioenerg. Biomemb. 22(6):789-810); tryptophan synthase (Zhao et al. (1995) J. Biol. Chem. 270(11):6081-6087); plastocyanin (Lawrence et al. (1997) J. Biol. Chem. 272(33):20357-20363); chorismate synthase (Schmidt et al. (1993) J. Biol. Chem. 268(36):27447-27457); and the light harvesting chlorophyll a/b binding protein (LHBP) (Lamppa et al. (1988) J. Biol. Chem. 263:14996-14999). See also Von Heijne et al. 15 (1991) PlantMol. Biol. Rep. 9:104-126; Clark et al. (1989) J Biol. Chem. 264:17544 17550; Della-Cioppa et al. (1987)Plant Physiol. 84:965-968; Romer et al. (1993) Biochem. Biophys. Res. Commun. 196:1414-1421; and Shah et al. (1986) Science 233:478-481. Methods for transformation of chloroplasts are known in the art. See, for 20 example, Svab et al. (1990) Proc. Nat. Acad Sci. USA 87:8526-8530; Svab and Maliga (1993) Proc. Nat. Acad. Sci. USA 90:913-917; Svab and Maliga (1993) EMBO J 12:601 606. The method relies on particle gun delivery of DNA containing a selectable marker and targeting of the DNA to the plastid genome through homologous recombination. Additionally, plastid transformation can be accomplished by transactivation of a silent 25 plastid-borne transgene by tissue-preferred expression of a nuclear-encoded and plastid directed RNA polymerase Such a system has been reported in McBride et al. (1994) Proc. Nat. Acad Sci. USA 91:7301-7305. The nucleic acids of interest to be targeted to the chloroplast may be optimized for expression in the chloroplast to account for differences in codon usage between the plant 30 nucleus and this organelle, In this manner, the nucleic acids of interest may be synthesized using chloroplast-preferred codons. See, for example, U.S. Patent No. 5,380,831, herein incorporated by reference. As disclosed herein, the AHASL nucleotide sequences of the invention find use in enhancing the herbicide tolerance of plants that comprise in their genomes a gene -37encoding a herbicide-tolerant AHASL protein. Such a gene may be an endogenous gene or a transgene. Additionally, in certain embodiments, the nucleic acid sequences of the present invention can be stacked with any combination of polynucleotide sequences of interest in order to create plants with a desired phenotype. For example, the 5 polynucleotides of the present invention may be stacked with any other polynucleotides encoding polypeptides having pesticidal and/or insecticidal activity, such as, for example, the Bacillus thuringiensis toxin proteins (described in U.S. Patent Nos. 5,366,892; 5,747,450; 5,737,514; 5,723,756; 5,593,881; and Geiser et al. (1986) Gene 48:109), The combinations generated can also include multiple copies of any one of the 10 polynucleotides of interest, It is recognized that with these nucleotide sequences, antisense constructions, complementary to at least a portion of the messenger RNA (mRNA) for the AHASL polynucleotide sequences can be constructed. Antisense nucleotides are constructed to hybridize with the corresponding mRNA. Modifications of the antisense sequences may 15 be made as long as the sequences hybridize to and interfere with expression of the corresponding mRNA. In this manner, antisense constructions having 70%, preferably 80%, more preferably 85% sequence identity to the corresponding antisensed sequences may be used. Furthermore, portions of the antisense nucleotides may be used to disrupt the expression of the target gene. Generally, sequences of at least 50 nucleotides, 100 20 nucleotides, 200 nucleotides, or greater may be used, The nucleotide sequences of the present invention may also be used in the sense orientation to suppress the expression of endogenous genes in plants. Methods for suppressing gene expression in plants using nucleotide sequences in the sense orientation are known in the art The methods generally involve transforming plants with a DNA 25 construct comprising a promoter that drives expression in a plant operably linked to at least a portion of a nucleotide sequence that corresponds to the transcript of the endogenous gene. Typically, such a nucleotide sequence has substantial sequence identity to the sequence of the transcript of the endogenous gene, preferably greater than about 65% sequence identity, more preferably greater than about 85% sequence identity, 30 most preferably greater than about 95% sequence identity. See, U.S. Patent Nos, 5,283,184 and 5,034,323; herein incorporated by reference, While the herbicide-resistant AHASL1 polynucleotides of the invention find use as selectable maker genes for plant transformation, the expression cassettes of the invention can include another selectable marker gene for the selection of transformed cells. Selectable -38marker genes, including those of the present invention, are utilized for the selection of transformed cells or tissues. Marker genes include, but are not limited to, genes encoding antibiotic resistance, such as those encoding neomycin phosphotransferase II (NEO) and hygromycin phosphotransferase (HPT), as well as genes conferring resistance to herbicidal 5 compounds, such as glufosinate ammonium, bromoxynil, imidazolinones, and 2,4 dichlorophenoxyacetate (2,4-D). See generally, Yarranton (1992) Curr. Opin. Biotech. 3:506-5 11; Christopherson et al. (1992) Proc. Nal. Acad Sci. USA 89:6314-6318; Yao et al. (1992) Cell71:63-72; Reznikoff (1992)Mol Microbiol. 6:2419-2422; Barkley et al. (1980) in The Operon, pp. 177-220; Hu et al. (1987) Cell 48:55 5-566; Brown et al. (1987) Cell 10 49:603-612; Figge et al. (1988) Cell 52:713-722; Deuschle et al. (1989) Proc. Nal. Acad Ad. USA 86:5400-5404; Fuerst et al. (1989) Proc. Nai. Acad Sci, USA 86:2549-2553; Deuschle et al. (1990) Science 248:480-483; Gossen (1993) Ph.D. Thesis, University of Heidelbeg;Reines et al. (1993) Proc. Nal. Acad Sci. USA 90:1917-1921; Labow et al. (1990) Mdol. Cell. Biol. 10:3343-33 56; Zambretti et al. (1992) Proc. Natd. Acad Sci. USA 15 89:3952-3956; Baim et al. (1991) Proc. Nal. Acad Sci. USA 88:5072-5 076; Wyborski et al. (1991) Nucleic Acids Res. 19:4647-4653; Hillenand-Wissman (1989) Topics Mol. Struc Biol. 10:143-162; Degenkolb et al. (1991) Antimicrob. Agents Chemother 35:1591-1595; Kleinschnidt et al. (1988) Biochemistry 27:1094-1104; Bonin (1993) Ph.D. Thesis, University of Heidelberg; Gossen etal. (1992) Proc. Nal. Acad Sci. USA 89:5547-5551; 20 Olivaet al. (1992) Antimicrob. Agents Chemother. 36:913-919; Hlavkaet al. (1985) Handbook ofExperimental Pharmacology, Vol. 78 ( Springer-Verlag, Berlin); Gill et al, (1988) Nature 334:721-724. Such disclosures are herein incorporated by reference. The above list of selectable marker genes is not meant to be limiting. Any selectable marker gene can be used in the present invention. 25 The isolated polynucleotide molecules comprising nucleotide sequence that encode the AHASL proteins of the invention can be used in vectors to transform plants so that the plants created have enhanced resistant to herbicides, particularly imidazolinone herbicides. The isolated AHASL polynucleotide molecules of the invention can be used in vectors alone or in combination with a nucleotide sequence encoding the small subunit 30 of the AHAS (AHASS) enzyme in conferring herbicide resistance in plants. See, U.S. Patent No. 6,348,643; which is herein incorporated by reference. The invention also relates to a plant expression vector comprising a promoter that drives expression in a plant operably linked to an isolated polynucleotide molecule of the invention. The isolated polynucleotide molecule comprises a nucleotide sequence -39encoding an AHASL protein, particularly an AHASL protein comprising an amino sequence that is set forth in SEQ ID NO: 2 or 4, or a functional fragment and variant thereof. The plant expression vector of the invention does not depend on a particular promoter, only that such a promoter is capable of driving gene expression in a plant cell. 5 Preferred promoters include constitutive promoters and tissue-preferred promoters. The transformation vectors of the invention can be used to produce plants transformed with a gene of interest. The transformation vector will comprise a selectable marker gene of the invention and a gene of interest to be introduced and typically expressed in the transformed plant. Such a selectable marker gene comprises a herbicide 10 resistant AHASL polynucleotide of the invention operably linked to a promoter that drives expression in a host cell. For use in plants and plant cells, the transformation vector comprises a selectable marker gene comprising a herbicide-resistant AHASL polynucleotide of the invention operably linked to a promoter that drives expression in a plant cell. 15 The genes of interest of the invention vary depending on the desired outcome. For example, various changes in phenotype can be of interest including modifying the fatty acid composition in a plant, altering the amino acid content of a plant, altering a plant's insect and/or pathogen defense mechanisms, and the like. These results can be achieved by providing expression of heterologous products or increased expression of endogenous 20 products in plants. Alternatively, the results can be achieved by providing for a reduction of expression of one or more endogenous products, particularly enzymes or cofactors in the plant. These changes result in a change in phenotype of the transformed plant. In one embodiment of the invention, the genes of interest include insect resistance genes such as, for example, Bacillus thuringiensis toxin protein genes (U.S. Patent Nos. 25 5,366,892; 5,747,450; 5,736,514; 5,723,756; 5,593,881; and Geiser et al. (1986) Gene 48:109). The AHASL proteins or polypeptides of the invention can be purified from, for example, sunflower plants and can be used in compositions. Also, an isolated polynucleotide molecule encoding an AHASL protein of the invention can be used to 30 express an AHASL protein of the invention in a microbe such as E. coli or a yeast The expressed AHASL protein can be purified from extracts of E. coli or yeast by any method known to those of ordinary skill in the art. The invention also relates to a method for creating a transgenic plant that is resistant to herbicides, comprising transforming a plant with a plant expression vector -40comprising a promoter that drives expression in a plant operably linked to an isolated polynucleotide molecule of the invention. The isolated polynucleotide molecule comprises a nucleotide sequence encoding an AHASL protein of the invention, particularly an AHASL protein comprising: an amino sequence that is set forth in SEQ ID 5 NO: 2, an amino acid sequence encoded by SEQ ID NO: 1, or a functional fragment and variant of said amino acid sequences. The invention also relates to the non-transgenic sunflower plants, transgenic plants produced by the methods of the invention, and progeny and other descendants of such non-transgenic and transgenic plants, which plants exhibit enhanced or increased 10 resistance to herbicides that interfere with the AHAS enzyme, particularly imidazolinone and sulfonylurea herbicides. The AHASL polynucleotides of the invention, particularly those encoding herbicide-resistant AHASL proteins, find use in methods for enhancing the resistance of herbicide-tolerant plants. In one embodiment of the invention, the herbicide-tolerant 15 plants comprise a herbicide-tolerant or herbicide-resistant AHASL protein. The herbicide-tolerant plants include both plants transformed with a herbicide-tolerant AHASL nucleotide sequences and plants that comprise in their genomes an endogenous gene that encodes a herbicide-tolerant AHASL protein. Nucleotide sequences encoding herbicide-tolerant AHASL proteins and herbicide-tolerant plants comprising an 20 endogenous gene that encodes a herbicide-tolerant AHASL protein include the polynucleotides and plants of the present invention and those that are known in the art. See, for example, U.S. Patent Nos. 5,013,659, 5,731,180, 5,767,361, 5,545,822, 5,736,629, 5,773,703, 5,773,704, 5,952,553 and 6,274,796; all of which are herein incorporated by reference. Such methods for enhancing the resistance of herbicide 25 tolerant plants comprise transforming a herbicide-tolerant plant with at least one polynucleotide construction comprising a promoter that drives expression in a plant cell that is operably linked to a herbicide-resistant AHASL polynucleotide of the invention, particularly the polynucleotide encoding a herbicide-resistant AHASL protein set forth in SEQ ID NO: 1, polynucleotides encoding the amino acid sequence set forth in SEQ ID 30 NO: 2, and fragments and variants said polynucleotides that encode polypeptides comprising herbicide-resistant AHAS activity, Numerous plant transformation vectors and methods for transforming plants are available. See, for example, An, G. et al. (1986) Plant Pysiol., 81:301-305; Fry, J., et al. (1987) Plant Cell Rep. 6:321-325; Block, M. (1988) Theor. Apple Genet.76:767-774; -41- Hinchee, et al. (1990) Stadler. Genet Synp.203212.203-212; Cousins, et a/. (1991) Aust. J Plant Physiol. 18:481-494; Chee, P. P. and Slightom, J. L. (1992) Gene.118:255-260; Christou, et al. (1992) Trend. Biotechnol. 10:239-246; D'Halluin, et al. (1992) Bio/Technol. 10:309-314; Dhir, et al. (1992) Plant Physiol. 99:81-88; Casas et al, (1993) 5 Proc. Nat. Acad Sci. USA 90:11212-11216; Christou, P. (1993) In Vitro Cell. Dev. Biol, Plant; 29P: 119-124; Davies, et al. (1993) Plant Cell Rep. 12:180-183; Dong, J. A. and Mchughen, A. (1993) Plant Sci. 91:139-148; Franklin, C. I. and Trieu, T. N. (1993) Plant. Physiol. 102:167; Golovkin, et al. (1993) Plant Sci. 90:41-52; Guo Chin Sci. Bull. 38:2072-2078; Asano, et al. (1994) Plant CellRep. 13; Ayeres N. M. and Park, W. D. 10 (1994) Crit. Rev. Plant. Sci. 13:219-239; Barcelo, et al. (1994) Plant. J. 5:583-592; Becker, et al. (1994) Plant. J. 5:299-307; Borkowska et al. (1994) Acta. Physiol Plant. 16:225-230; Christou, P. (1994) Agro. Food. Ind. Hi Tech. 5: 17-27; Eapen et al. (1994) Plant Cell Rep, 13:582-586; Hartman, et al. (1994) Bio-Technology 12: 919923; Ritala, et al. (1994) Plant. Mo!. Biol. 24:317-325; and Wan, Y. C. and Lemaux, P. G. (1994) Plant 15 Physiol 104:3748. The methods of the invention involve introducing a polynucleotide construct into a plant. By "introducing" is intended presenting to the plant the polynucleotide construct in such a manner that the construct gains access to the interior of a cell of the plant. The methods of the invention do not depend on a particular method for introducing a 20 polynucleotide construct to a plant, only that the polynucleotide construct gains access to the interior of at least one cell of the plant. Methods for introducing polynucleotide constructs into plants are known in the art including, but not limited to, stable transformation methods, transient transformation methods, and virus-mediated methods, By "stable transformation" is intended that the polynucleotide construct 25 introduced into a plant integrates into the genome of the plant and is capable of being inherited by progeny thereof. By "transient transformation" is intended that a polynucleotide construct introduced into a plant does not integrate into the genome of the plant. For the transformation of plants and plant cells, the nucleotide sequences of the 30 invention are inserted using standard techniques into any vector known in the art that is suitable for expression of the nucleotide sequences in a plant or plant cell. The selection of the vector depends on the preferred transformation technique and the target plant species to be transformed. In an embodiment of the invention, an AHASLI nucleotide sequence is operably linked to a plant promoter that is known for high-level expression in -42a plant cell, and this construct is then introduced into a plant that is susceptible to an imidazolinone herbicide and a transformed plant is regenerated. The transformed plant is tolerant to exposure to a level of an imidazolinone herbicide that would kill or significantly injure an untransformed plant. This method can be applied to any plant 5 species; however, it is most beneficial when applied to crop plants. Methodologies for constructing plant expression cassettes and introducing foreign nucleic acids into plants are generally known in the art and have been previously described. For example, foreign DNA can be introduced into plants, using tumor inducing (Ti) plasmid vectors. Other methods utilized for foreign DNA delivery involve 10 the use of PEG mediated protoplast transformation, electroporation, microinjection whiskers, and biolistics or microprojectile bombardment for direct DNA uptake. Such methods are known in the art. (U.S. Pat. No. 5,405,765 to Vasil et al.; Bilang et al. (1991) Gene 100: 247-250; Scheid et al., (1991)Mol. Gen. Genet., 228: 104-112; Guerche et al., (1987) Plant Science 52: 111-116; Neuhause et al,, (1987) Theor. Apple Genet. 75: 30-36; 15 Klein et al., (1987) Nature 327: 70-73; Howell et al., (1980) Science 208:1265; Horsch et al., (1985) Science 227: 1229-123 1; DeBlock et al., (1989) Plant Physiology 91: 694-701; Methodsfor Plant Molecular Biology (Weissbach and Weissbach, eds.) Academic Press, Inc. (1988) and Methods in Plant Molecular Biology (Schuler and Zielinski, eds.) Academic Press, Inc. (1989). The method of transformation depends upon the plant cell 20 to be transformed, stability of vectors used, expression level of gene products and other parameters. Other suitable methods of introducing nucleotide sequences into plant cells and subsequent insertion into the plant genome include microinjection as Crossway et al. (1986) Biotechniques 4:320-334, electroporation as described by Riggs et al. (1986) Proc. 25 Nat!. Acad Sci. USA 83:5602-5606, Agrobacteriuni-mediated transformation as described by Townsend et al., U.S. Patent No. 5,563,055, Zhao et al., U.S. Patent No. 5,981,840, direct gene transfer as described by Paszkowski et al. (1984) EMBO J. 3:2717-2722, and ballistic particle acceleration as described in, for example, Sanford et al., U.S. Patent No. 4,945,050; Tomes et al., U.S. Patent No. 5,879,918; Tomes et al., U.S. Patent No. 30 5,886,244; Bidney et al., US. Patent No. 5,932,782; Tomes et al. (1995) "Direct DNA Transfer into Intact Plant Cells via Microprojectile Bombardment," in Plant Cell, Tissue, and Organ Culture: Fundamental Methods, ed, Gamborg and Phillips (Springer-Verlag, Berlin); McCabe et al. (1988) Biotechnology 6:923-926); and Lec1 transformation (WO 00/28058). Also see, Weissinger et al. (1988) Ann. Rev. Genet. 22:421-477; Sanford et - 43 al. (1987) Particulate Science and Technology 5:27-37 (onion); Christou et al. (1988) Plant Physiol. 87:671-674 (soybean); McCabe et al. (1988) Bio/Technology 6:923-926 (soybean); Finer and McMullen (1991) In Vitro Cell Dev. Biol. 27P: 175-182 (soybean); Singh et al. (1998) Theor. Apple. Genet. 96:319-324 (soybean); Datta et al. (1990) 5 Biotechnology 8:736-740 (rice); Klein et al. (1988) Proc. Natl. Acad Sci. USA 85:4305-4309 (maize); Klein et al. (1988) Biotechnology 6:559-563 (maize); Tomes, U.S. Patent No. 5,240,855; Buising et al., U.S. Patent Nos. 5,322,783 and 5,324,646; Tomes et al. (1995) "Direct DNA Transfer into Intact Plant Cells via Microprojectile Bombardment," in Plant Cell, Tissue, and Organ Culture: Fundamental Methods, ed. 10 Gamborg (Springer-Verlag, Berlin) (maize); Klein et al. (1988) Plant Physiol. 91:440-444 (maize); Fromm et al. (1990) Biotechnology 8:833-839 (maize); Hooykaas Van Slogteren et al. (1984) Nature (London) 311:763-764; Bowen et al., U.S. Patent No. 5,736,369 (cereals); Bytebier et al. (1987) Proc. Natl. Acad Sci. USA 84:5345-5349 (Liliaceae); De Wet et al. (1985) in The Experimental Manipulation of Ovule Tissues, ed. 15 Chapman et al. (Longman, New York), pp. 197-209 (pollen); Kaeppler et al. (1990) Plant Cell Reports 9:415-418 and Kaeppler et al. (1992) Theor. Apple. Genet. 84:560-566 (whisker-mediated transformation); D'Halluin et al. (1992) Plant Cell 4:1495-1505 (electroporation); Li et al. (1993) Plant Cell Reports 12:250-255 and Christou and Ford (1995)Annals of Botany 75:407-413 (rice); Osjoda et al. (1996) Nature Biotechnology 20 14:745-750 (maize via Agrobacterium tumefaciens); all of which are herein incorporated by reference. The polynucleotides of the invention may be introduced into plants by contacting plants with a virus or viral nucleic acids. Generally, such methods involve incorporating a polynucleotide construct of the invention within a viral DNA or RNA molecule. It is 25 recognized that the an AHASL protein of the invention may be initially synthesized as part of a viral polyprotein, which later may be processed by proteolysis in vivo or in vitro to produce the desired recombinant protein, Further, it is recognized that promoters of the invention also encompass promoters utilized for transcription by viral RNA polymerases. Methods for introducing polynucleotide constructs into plants and expressing a protein 30 encoded therein, involving viral DNA or RNA molecules, are known in the art. See, for example, U.S. Patent Nos, 5,889,191, 5,889,190, 5,866,785, 5,589,367 and 5,316,931; herein incorporated by reference. The cells that have been transformed may be grown into plants in accordance with conventional ways. See, for example, McCormick et al. (1986) Plant Cell Reports 5:81 - 44- 84. These plants may then be grown, and either pollinated with the same transformed strain or different strains, and the resulting hybrid having constitutive expression of the desired phenotypic characteristic identified. Two or more generations may be grown to ensure that expression of the desired phenotypic characteristic is stably maintained and 5 inherited and then seeds harvested to ensure expression of the desired phenotypic characteristic has been achieved. In this manner, the present invention provides transformed seed (also referred to as "transgenic seed") having a polynucleotide construct of the invention, for example, an expression cassette of the invention, stably incorporated into their genome. 10 The present invention may be used for transformation of any plant species, including, but not limited to, monocots and dicots. Examples of plant species of interest include, but are not limited to, corn or maize (Zea mays), Brassica sp. (e.g., B. napus, B. rapa, B. juncea), particularly those Brassica species useful as sources of seed oil, alfalfa (Medicago sativa), rice (Oryza sativa), rye (Secale cereale), sorghum (Sorghumn bicolor, 15 Sorghum vulgare), millet (e.g., pearl millet (Pennisetum glaucum), proso millet (Panicum miliaceum), foxtail millet (Setaria italica), finger millet (Eleusine coracana)), sunflower (Heianthus anuus), safflower (Carthamus tinctorius), wheat (Triticum aestivum, T. Turgidum ssp. durum), soybean (Glycine max), tobacco (Nicotiana tabacum), potato (Solanum tuberosum), peanuts (Arachis hypogaea), cotton (Gossypium barbadense, 20 Gossypium hirsutum), sweet potato (pomoea batatus), cassava (Manihot esculenta), coffee (Coffea spp.), coconut (Cocos nucifera), pineapple (Ananas comosus), citrus trees (Citrus spp.), cocoa (Theobroma cacao), tea (Camellia sinensis), banana (Musa spp.), avocado (Persea americana), fig (Ficus casica), guava (Psidium guajava), mango (Mangifera indica), olive (Olea europaea), papaya (Caricapapaya), cashew (Anacardium occidentale), 25 macadamia (Macadamia integrifolia), almond (Prunus amygdalus), sugar beets (Beta vulgaris), sugarcane (Saccharum spp.), oats, barley, vegetables, ornamentals, and conifers. Preferably, plants of the present invention are crop plants (for example, sunflower, Brassica sp., cotton, sugar beet, soybean, peanut, alfalfa, safflower, tobacco, corn, rice, wheat, rye, barley triticale, sorghum, millet, etc.). 30 The herbicide-resistant plants of the invention find use in methods for controlling weeds. Thus, the present invention further provides a method for controlling weeds in the vicinity of a herbicide-resistant plant of the invention. The method comprises applying an effective amount of a herbicide to the weeds and to the herbicide-resistant plant, wherein the plant has increased resistance to at least one herbicide, particularly an imidazolinone - 45 or sulfonylurea herbicide, when compared to a wild-type plant. In such a method for controlling weeds, the herbicide-resistant plants of the invention are preferably crop plants, including, but not limited to, sunflower, alfalfa, Brassica sp., soybean, cotton, safflower, peanut, tobacco, tomato, potato, wheat, rice, maize, sorghum, barley, rye, millet, 5 and sorghum. By providing plants having increased resistance to herbicides, particularly imidazolinone and sulfonylurea herbicides, a wide variety of formulations can be employed for protecting plants from weeds, so as to enhance plant growth and reduce competition for nutrients. A herbicide can be used by itself for pre-emergence, post 10 emergence, pre-planting and at planting control of weeds in areas surrounding the plants described herein or an imidazolinone herbicide formulation can be used that contains other additives. The herbicide can also be used as a seed treatment. Additives found in an imidazolinone or sulfonylurea herbicide formulation include other herbicides, detergents, adjuvants, spreading agents, sticking agents, stabilizing agents, or the like. The herbicide 15 formulation can be a wet or dry preparation and can include, but is not limited to, flowable powders, emulsifiable concentrates and liquid concentrates. The herbicide and herbicide formulations can be applied in accordance with conventional methods, for example, by spraying, irrigation, dusting, or the like. The present invention provides non-transgenic and transgenic seeds with 20 increased tolerance to at least one herbicide, particularly an AHAS-inhibiting herbicide, more particularly imidazolinone and sulfonylurea herbicides. Such seeds include, for example, non-transgenic sunflower seeds comprising the herbicide-tolerance characteristics of the sunflower plant S4897, the sunflower plant GM40, the sunflower plant GM1606, the sunflower plant with ATCC Patent Deposit Number PTA-6716, or the 25 sunflower plant with ATCC Patent Deposit Number PTA-7606, and transgenic seeds comprising a polynucleotide molecule of the invention that encodes a herbicide-resistant AHASL protein. The present invention provides methods for producing a herbicide-resistant plant, particularly a herbicide-resistant sunflower plant, through conventional plant breeding 30 involving sexual reproduction. The methods comprise crossing a first plant that is resistant to a herbicide to a second plant that is not resistant to the herbicide. The first plant can be any of the herbicide resistant plants of the present invention including, for example, transgenic plants comprising at least one of the polynucleotide molecules of the present invention that encode a herbicide resistant AHASL protein and non-transgenic -46sunflower plants that comprise the herbicide-tolerance characteristics of the sunflower plant S4897, the sunflower plant GM40, the sunflower plant GMI 606, the sunflower plant with ATCC Patent Deposit Number PTA-6716, or the sunflower plant with ATCC Patent Deposit Number PTA-7606. The second plant can be any plant that is capable of 5 producing viable progeny plants (i.e., seeds) when crossed with the first plant. Typically, but not necessarily, the first and second plants are of the same species. The methods of the invention can further involve one or more generations of backcrossing the progeny plants of the first cross to a plant of the same line or genotype as either the first or second plant. Alternatively, the progeny of the first cross or any subsequent cross can be crossed 10 to a third plant that is of a different line or genotype than either the first or second plant. The methods of the invention can additionally involve selecting plants that comprise the herbicide tolerance characteristics of the first plant. The present invention further provides methods for increasing the herbicide resistance of a plant, particularly a herbicide-resistant sunflpower plant, through 15 conventional plant breeding involving sexual reproduction. The methods comprise crossing a first plant that is resistant to a herbicide to a second plant that may or may not be resistant to the herbicide or may be resistant to different herbicide or herbicides than the first plant. The first plant can be any of the herbicide resistant plants of the present invention including, for example, transgenic plants comprising at least one of the 20 polynucleotide molecules of the present invention that encode a herbicide-resistant AHASL protein and non-transgenic sunflower plants that comprise the herbicide tolerance characteristics of the sunflower plant S4897, the sunflower plant GM40, the sunflower plant GMl 606, the sunflower plant with ATCC Patent Deposit Number PTA 6716, or the sunflower plant with ATCC Patent Deposit Number PTA-7606. The second 25 plant can be any plant that is capable of producing viable progeny plants (i.e., seeds) when crossed with the first plant. Typically, but not necessarily, the first and second plants are of the same species. The progeny plants produced by this method of the present invention have increased resistance to a herbicide when compared to either the first or second plant or both. When the first and second plants are resistant to different 30 herbicides, the progeny plants will have the combined herbicide tolerance characteristics of the first and second plants. The methods of the invention can further involve one or more generations of backcrossing the progeny plants of the first cross to a plant of the same line or genotype as either the first or second plant. Alternatively, the progeny of the first cross or any subsequent cross can be crossed to a third plant that is of a different line - 47 or genotype than either the first or second plant. The methods of the invention can additionally involve selecting plants that comprise the herbicide tolerance characteristics of the first plant, the second plant, or both the first and the second plant. The plants of the present invention can be transgenic or non-transgenic An 5 example of a non-transgenic sunflower plant having increased resistance to imidazolinone is the sunflower plant sunflower plant S4897, the sunflower plant GM40, the sunflower plant GM1606, the sunflower plant with ATCC Patent Deposit Number PTA-6716, or the sunflower plant with ATCC Patent Deposit Number PTA-7606; or mutant, recombinant, or a genetically engineered derivative of the sunflower plant S4897, the sunflower plant 10 GM40, the sunflower plant GM1606, the sunflower plant with ATCC Patent Deposit Number PTA-6716, or the sunflower plant with ATCC Patent Deposit Number PTA 7606; or of any progeny of the sunflower plant S4897, the sunflower plant GM40, the sunflower plant GM1606, the sunflower plant with ATCC Patent Deposit Number PTA 6716, or the sunflower plant with ATCC Patent Deposit Number PTA-7606; or a plant 15 that is a progeny of any of these plants; or a plant that comprises the herbicide tolerance characteristics of the sunflower plant S4897, the sunflower plant GM40, the sunflower plant GMI 606, the sunflower plant with ATCC Patent Deposit Number PTA-6716, or the sunflower plant with ATCC Patent Deposit Number PTA-7606. The present invention also provides plants, plant organs, plant tissues, plant cells, 20 seeds, and non-human host cells that are transformed with the at least one polynucleotide molecule, expression cassette, or transformation vector of the invention. Such transformed plants, plant organs, plant tissues, plant cells, seeds, and non-human host cells have enhanced tolerance or resistance to at least one herbicide, at levels of the herbicide that kill or inhibit the growth of an untransformed plant, plant tissue, plant cell, 25 or non-human host cell, respectively. Preferably, the transformed plants, plant tissues, plant cells, and seeds of the invention are Arabidopsis thaliana and crop plants. The present invention provides methods that involve the use of at least one AHAS-inhibiting herbicide selected from the group consisting of imidazolinone herbicides, sulfonylurea herbicides, triazolopyrimidine herbicides, 30 pyrimidinyloxybenzoate herbicides, sulfonylamino-carbonyltriazolinone herbicides, and mixtures thereof. In these methods, the AHAS-inhibiting herbicide can be applied by any method known in the art including, but not limited to, seed treatment, soil treatment, and foliar treatment. - 48 - Prior to application, the AHAS-inhibiting herbicide can be converted into the customary formulations, for example solutions, emulsions, suspensions, dusts, powders, pastes and granules. The use form depends on the particular intended purpose; in each case, it should ensure a fine and even distribution of the compound according to the 5 invention. The formulations are prepared in a known manner (see e.g. for review US 3,060,084, EP-A 707 445 (for liquid concentrates), Browning, "Agglomeration", Chemical Engineering, Dec. 4, 1967, 147-48, Perry's Chemical Engineer's Handbook, 4th Ed., McGraw-Hill, New York, 1963, pages 8-57 and et seq. WO 91/13546, US 10 4,172,714, US 4,144,050, US 3,920,442, US 5,180,587, US 5,232,701, US 5,208,030, GB 2,095,558, US 3,299,566, Klingman, Weed Control as a Science, John Wiley and Sons, Inc., New York, 1961, Hance et al., Weed Control Handbook, 8th Ed., Blackwell Scientific Publications, Oxford, 1989 and Mollet, H., Grubemann, A., Formulation technology, Wiley VCH Verlag GmbH, Weinheim (Germany), 2001, 2. D. A. Knowles, 15 Chemistry and Technology of Agrochemical Formulations, Kluwer Academic Publishers, Dordrecht, 1998 (ISBN 0-7514-0443-8), for example by extending the active compound with auxiliaries suitable for the formulation of agrochemicals, such as solvents and/or carriers, if desired emulsifiers, surfactants and dispersants, preservatives, antifoaming agents, anti-freezing agents, for seed treatment formulation also optionally colorants 20 and/or binders and/or gelling agents. Examples of suitable solvents are water, aromatic solvents (for example Solvesso products, xylene), paraffins (for example mineral oil fractions), alcohols (for example methanol, butanol, pentanol, benzyl alcohol), ketones (for example cyclohexanone, gamma-butyrolactone), pyrrolidones (NMP, NOP), acetates (glycol diacetate), glycols, 25 fatty acid dimethylamides, fatty acids and fatty acid esters. In principle, solvent mixtures may also be used. Examples of suitable carriers are ground natural minerals (for example kaolins, clays, talc, chalk) and ground synthetic minerals (for example highly disperse silica, silicates). 30 Suitable emulsifiers are nonionic and anionic emulsifiers (for example polyoxyethylene fatty alcohol ethers, alkylsulfonates and arylsulfonates). Examples of dispersants are lignin-sulfite waste liquors and methylcellulose. Suitable surfactants used are alkali metal, alkaline earth metal and ammonium salts of lignosulfonic acid, naphthalenesulfonic acid, phenolsulfonic acid, -49dibutylnaphthalenesulfonic acid, alkylarylsulfonates, alkyl sulfates, alkylsulfonates, fatty alcohol sulfates, fatty acids and sulfated fatty alcohol glycol ethers, furthermore condensates of sulfonated naphthalene and naphthalene derivatives with formaldehyde, condensates of naphthalene or of naphthalenesulfonic acid with phenol and 5 formaldehyde, polyoxyethylene octylphenol ether, ethoxylated isooctylphenol, octylphenol, nonylphenol, alkylphenol polyglycol ethers, tributylphenyl polyglycol ether, tristearylphenyl polyglycol ether, alkylaryl polyether alcohols, alcohol and fatty alcohol ethylene oxide condensates, ethoxylated castor oil, polyoxyethylene alkyl ethers, ethoxylated polyoxypropylene, lauryl alcohol polyglycol ether acetal, sorbitol esters, 10 lignosulfite waste liquors and methylcellulose. Substances which are suitable for the preparation of directly sprayable solutions, emulsions, pastes or oil dispersions are mineral oil fractions of medium to high boiling point, such as kerosene or diesel oil, furthermore coal tar oils and oils of vegetable or animal origin, aliphatic, cyclic and aromatic hydrocarbons, for example toluene, xylene, 15 paraffin, tetrahydronaphthalene, alkylated naphthalenes or their derivatives, methanol, ethanol, propanol, butanol, cyclohexanol, cyclohexanone, isophorone, highly polar solvents, for example dimethyl sulfoxide, N-methylpyrrolidone or water. Also anti-freezing agents such as glycerin, ethylene glycol, propylene glycol and bactericides such as can be added to the formulation. 20 Suitable antifoaming agents are for example antifoaming agents based on silicon or magnesium stearate. Suitable preservatives are for example Dichlorophen und enzylalkoholhemiformal. Seed Treatment formulations may additionally comprise binders and optionally 25 colorants. Binders can be added to improve the adhesion of the active materials on the seeds after treatment. Suitable binders are block copolymers EO/PO surfactants but also polyvinylalcoholsl, polyvinylpyrrolidones, polyacrylates, polymethacrylates, polybutenes, polyisobutylenes, polystyrene, polyethyleneamines, polyethyleneamides, 30 polyethyleneimines (Lupasol@, Polymin@), polyethers, polyurethans, polyvinylacetate, tylose and copolymers derived from these polymers. Optionally, also colorants can be included in the formulation. Suitable colorants or dyes for seed treatment formulations are Rhodamin B, CI. Pigment Red 112, C.I. Solvent Red 1, pigment blue 15:4, pigment blue 15:3, pigment blue 15:2, pigment blue 15:1, -50pigment blue 80, pigment yellow 1, pigment yellow 13, pigment red 112, pigment red 48:2, pigment red 48:1, pigment red 57:1, pigment red 53:1, pigment orange 43, pigment orange 34, pigment orange 5, pigment green 36, pigment green 7, pigment white 6, pigment brown 25, basic violet 10, basic violet 49, acid red 51, acid red 52, acid red 14, 5 acid blue 9, acid yellow 23, basic red 10, basic red 108. An example of a suitable gelling agent is carrageen (Satiagel*) Powders, materials for spreading, and dustable products can be prepared by mixing or concomitantly grinding the active substances with a solid carrier. Granules, for example coated granules, impregnated granules and homogeneous 10 granules, can be prepared by binding the active compounds to solid carriers. Examples of solid carriers are mineral earths such as silica gels, silicates, talc, kaolin, attaclay, limestone, lime, chalk, bole, less, clay, dolomite, diatomaceous earth, calcium sulfate, magnesium sulfate, magnesium oxide, ground synthetic materials, fertilizers, such as, for example, ammonium sulfate, ammonium phosphate, ammonium nitrate, ureas, and 15 products of vegetable origin, such as cereal meal, tree bark meal, wood meal and nutshell meal, cellulose powders and other solid carriers. In general, the formulations comprise from 0.01 to 95% by weight, preferably from 0.1 to 90% by weight, of the AHAS-inhibiting herbicide. In this case, the AHAS inhibiting herbicides are employed in a purity of from 90% to 100% by weight, preferably 20 95% to 100% by weight (according to NMR spectrum). For seed treatment purposes, respective formulations can be diluted 2-10 fold leading to concentrations in the ready to use preparations of 0.01 to 60% by weight active compound by weight, preferably 0.1 to 40% by weight. The AHAS-inhibiting herbicide can be used as such, in the form of their 25 formulations or the use forms prepared therefrom, for example in the form of directly sprayable solutions, powders, suspensions or dispersions, emulsions, oil dispersions, pastes, dustable products, materials for spreading, or granules, by means of spraying, atomizing, dusting, spreading or pouring. The use forms depend entirely on the intended purposes; they are intended to ensure in each case the finest possible distribution of the 30 AHAS-inhibiting herbicide according to the invention. Aqueous use forms can be prepared from emulsion concentrates, pastes or wettable powders (sprayable powders, oil dispersions) by adding water. To prepare emulsions, pastes or oil dispersions, the substances, as such or dissolved in an oil or solvent, can be homogenized in water by means of a wetter, tackifier, dispersant or - 51 emulsifier. However, it is also possible to prepare concentrates composed of active substance, wetter, tackifier, dispersant or emulsifier and, if appropriate, solvent or oil, and such concentrates are suitable for dilution with water. The active compound concentrations in the ready-to-use preparations can be 5 varied within relatively wide ranges. In general, they are from 0.0001 to 10%, preferably from 0.01 to 1% per weight. The AHAS-inhibiting herbicide may also be used successfully in the ultra-low volume process (ULV), it being possible to apply formulations comprising over 95% by weight of active compound, or even to apply the active compound without additives. 10 The following are examples of formulations: 1. Products for dilution with water for foliar applications. For seed treatment purposes, such products may be applied to the seed diluted or undiluted. A) Water-soluble concentrates (SL, LS) Ten parts by weight of the AHAS-inhibiting herbicide are dissolved in 15 90 parts by weight of water or a water-soluble solvent. As an alternative, wetters or other auxiliaries are added. The AHAS-inhibiting herbicide dissolves upon dilution with water, whereby a formulation with 10 % (w/w) of AHAS-inhibiting herbicide is obtained. B) Dispersible concentrates (DC) 20 Twenty parts by weight of the AHAS-inhibiting herbicide are dissolved in 70 parts by weight of cyclohexanone with addition of 10 parts by weight of a dispersant, for example polyvinylpyrrolidone. Dilution with water gives a dispersion, whereby a formulation with 20% (w/w) of AHAS-inhibiting herbicide is obtained. 25 C) Emulsifiable concentrates (EC) Fifteen parts by weight of the AHAS-inhibiting herbicide are dissolved in 7 parts by weight of xylene with addition of calcium dodecylbenzenesulfonate and castor oil ethoxylate (in each case 5 parts by weight). Dilution with water gives an emulsion, whereby a 30 formulation with 15% (w/w) of AHAS-inhibiting herbicide is obtained. D) Emulsions (EW, EO, ES) Twenty-five parts by weight of the AHAS-inhibiting herbicide are dissolved in 35 parts by weight of xylene with addition of calcium dodecylbenzenesulfonate and castor oil ethoxylate (in each case 5 parts -52by weight). This mixture is introduced into 30 parts by weight of water by means of an emulsifier machine (e.g. Ultraturrax) and made into a homogeneous emulsion. Dilution with water gives an emulsion, whereby a formulation with 25% (w/w) of AHAS-inhibiting herbicide is obtained. 5 E) Suspensions (SC, OD, FS) In an agitated ball mill, 20 parts by weight of the AHAS-inhibiting herbicide are comminuted with addition of 10 parts by weight of dispersants, wetters and 70 parts by weight of water or of an organic solvent to give a fine AHAS-inhibiting herbicide suspension. Dilution 10 with water gives a stable suspension of the AHAS-inhibiting herbicide, whereby a formulation with 20% (w/w) of AHAS-inhibiting herbicide is obtained. F) Water-dispersible granules and water-soluble granules (WG, SG) Fifty parts by weight of the AHAS-inhibiting herbicide are ground finely 15 with addition of 50 parts by weight of dispersants and wetters and made as water-dispersible or water-soluble granules by means of technical appliances (for example extrusion, spray tower, fluidized bed). Dilution with water gives a stable dispersion or solution of the AHAS-inhibiting herbicide, whereby a formulation with 50% (w/w) of AHAS-inhibiting 20 herbicide is obtained. G) Water-dispersible powders and water-soluble powders (WP, SP, SS, WS) Seventy-five parts by weight of the AHAS-inhibiting herbicide are ground in a rotor-stator mill with addition of 25 parts by weight of 25 dispersants, wetters and silica gel. Dilution with water gives a stable dispersion or solution of the AHAS-inhibiting herbicide, whereby a formulation with 75% (w/w) of AHAS-inhibiting herbicide is obtained. I) Gel-Formulation (GF) In an agitated ball mill, 20 parts by weight of the AHAS-inhibiting 30 herbicide are comminuted with addition of 10 parts by weight of dispersants, I part by weight of a gelling agent wetters and 70 parts by weight of water or of an organic solvent to give a fine AHAS-inhibiting herbicide suspension. Dilution with water gives a stable suspension of the AHAS-inhibiting herbicide, whereby a formulation with 20% (w/w) - 53 of AHAS-inhibiting herbicide is obtained. This gel formulation is suitable for us as a seed treatment. 2. Products to be applied undiluted for foliar applications. For seed treatment purposes, such products may be applied to the seed diluted. 5 A) Dustable powders (DP, DS) Five parts by weight of the AHAS-inhibiting herbicide are ground finely and mixed intimately with 95 parts by weight of finely divided kaolin. This gives a dustable product having 5% (w/w) of AHAS-inhibiting herbicide. 10 B) Granules (GR, FG, GG, MG) One-half part by weight of the AHAS-inhibiting herbicide is ground finely and associated with 95.5 parts by weight of carriers, whereby a formulation with 0.5% (w/w) of AHAS-inhibiting herbicide is obtained. Current methods are extrusion, spray-drying or the fluidized bed. This 15 gives granules to be applied undiluted for foliar use. Conventional seed treatment formulations include for example flowable concentrates FS, solutions LS, powders for dry treatment DS, water dispersible powders for slurry treatment WS, water-soluble powders SS and emulsion ES and EC and gel formulation GF. These formulations can be applied to the seed diluted or undiluted. 20 Application to the seeds is carried out before sowing, either directly on the seeds. In a preferred embodiment a FS formulation is used for seed treatment Typcially, a FS formulation may comprise 1-800 g/l of active ingredient, 1-200 g/l Surfactant, 0 to 200 g/l antifreezing agent, 0 to 400 g/l of binder, 0 to 200 g/l of a pigment and up to 1 liter of a solvent, preferably water. 25 The present invention non-transgenic and transgenic seeds of the herbicide resistant plants of the present invention. Such seeds include, for example, non-transgenic sunflower seeds comprising the herbicide-tolerance characteristics of the plant with NCIMB Accession Number NCIMB 41262, and transgenic seeds comprising a polynucleotide molecule of the invention that encodes an IMI protein. 30 For seed treatment, seeds of the herbicide resistant plants according of the present invention are treated with herbicides, preferably herbicides selected from the group consisting of AHAS-inhibiting herbicides such as amidosulfuron, azimsulfuron, bensulfuron, chlorimuron, chlorsulfuron, cinosulfuron, cyclosulfamuron, ethametsulfuron, ethoxysulfuron, flazasulfuron, flupyrsulfuron, foramsulfuron, - 54halosulfuron, imazosulfuron, iodosulfuron, mesosulfuron, metsulfuron, nicosulfuron, oxasulfuron, primisulfuron, prosulfuron, pyrazosulfuron, rimsulfuron, sulfometuron, sulfosulfuron, thifensulfuron, triasulfuron, tribenuron, trifloxysulfuron, triflusulfuron, tritosulfuron, imazamethabenz, imazamox, imazapic, imazapyr, imazaquin, imazethapyr, 5 cloransulam, diclosulam, florasulam, flumetsulam, metosulam, penoxsulam, bispyribac, pyriminobac, propoxycarbazone, flucarbazone, pyribenzoxim, pyriftalid, pyrithiobac, and mixtures thereof, or with a formulation comprising a AHAS-inhibiting herbicide. The term seed treatment comprises all suitable seed treatment techniques known in the art, such as seed dressing, seed coating, seed dusting, seed soaking, and seed 10 pelleting. In accordance with one variant of the present invention, a further subject of the invention is a method of treating soil by the application, in particular into the seed drill: either of a granular formulation containing the AHAS-inhibiting herbicide as a composition/formulation (e.g .a granular formulation, with optionally one or more solid 15 or liquid, agriculturally acceptable carriers and/or optionally with one or more agriculturally acceptable surfactants. This method is advantageously employed, for example, in seedbeds of cereals, maize, cotton, and sunflower. The present invention also comprises seeds coated with or containing with a seed treatment formulation comprising at least one AHAS-inhibiting herbicide selected from 20 the group consisting of amidosulfuron, azimsulfuron, bensulfuron, chlorimuron, chlorsulfuron, cinosulfuron, cyclosulfamuron, ethametsulfuron, ethoxysulfuron, flazasulfuron, flupyrsulfuron, foramsulfuron, halosulfuron, imazosulfuron, iodosulfuron, mesosulfuron, metsulfuron, nicosulfuron, oxasulfuron, primisulfuron, prosulfuron, pyrazosulfuron, rimsulfuron, sulfometuron, sulfosulfuron, thifensulfuron, triasulfuron, 25 tribenuron, trifloxysulfuron, triflusulfuron, tritosulfuron, imazamethabenz, imazamox, imazapic, imazapyr, imazaquin, imazethapyr, cloransulam, diclosulam, florasulam, flumetsulam, metosulam, penoxsulam, bispyribac, pyriminobac, propoxycarbazone, flucarbazone, pyribenzoxim, pyriftalid and pyrithiobac. The term seed embraces seeds and plant propagules of all kinds including but not 30 limited to true seeds, seed pieces, suckers, corms, bulbs, fruit, tubers, grains, cuttings, cut shoots and the like and means in a preferred embodiment true seeds. The term "coated with and/or containing" generally signifies that the active ingredient is for the most part on the surface of the propagation product at the time of application, although a greater or lesser part of the ingredient may penetrate into the - 55 propagation product, depending on the method of application. When the said propagation product is (re)planted, it may absorb the active ingredient. The seed treatment application with the AHAS-inhibiting herbicide or with a formulation comprising the AHAS-inhibiting herbicide is carried out by spraying or 5 dusting the seeds before sowing of the plants and before emergence of the plants. In the treatment of seeds, the corresponding formulations are applied by treating the seeds with an effective amount of the AHAS-inhibiting herbicide or a formulation comprising the AHAS-inhibiting herbicide, Herein, the application rates are generally from 0,1 g to 10 kg of the a.i. (or of the mixture of a.i. or of the formulation) per 100 kg 10 of seed, preferably from 1 g to 5 kg per 100 kg of seed, in particular from 1 g to 2.5 kg per 100 kg of seed. For specific crops such as lettuce the rate can be higher. The present invention provides a method for combating undesired vegetation or controlling weeds comprising contacting the seeds of the resistant plants according to the present invention before sowing and/or after pregermination with an AHAS-inhibiting 15 herbicide. The method can further comprise sowing the seeds, for example, in soil in a field or in a potting medium in greenhouse. The method finds particular use in combating undesired vegetation or controlling weeds in the immediate vicinity of the seed. The control of undesired vegetation is understood as meaning the killing of weeds and/or otherwise retarding or inhibiting the normal growth of the weeds. Weeds, in the 20 broadest sense, are understood as meaning all those plants which grow in locations where they are undesired. The weeds of the present invention include, for example, dicotyledonous and monocotyledonous weeds. Dicotyledonous weeds include, but are not limited to, weeds of the genera: Sinapis, Lepidium, Galium, Stellaria, Matricaria, Anthemis, Galinsoga, 25 Chenopodium, Urtica, Senecio, Amaranthus, Portulaca, Xanthium, Convolvulus, Ipomoea, Polygonum, Sesbania, Ambrosia, Cirsium, Carduus, Sonchus, Solanum, Rorippa, Rotala, Lindernia, Lamium, Veronica, Abutilon, Emex, Datura, Viola, Galeopsis, Papaver, Centaurea, Trifolium, Ranunculus, and Taraxacum. Monocotyledonous weeds include, but are not limited to, weeds of of the genera: 30 Echinochloa, Setaria, Panicum, Digitaria, Phleum, Poa, Festuca, Eleusine, Brachiaria, Lolium, Bromus, Avena, Cyperus, Sorghum, Agropyron, Cynodon, Monochoria, Fimbristyslis, Sagittaria, Eleocharis, Scirpus, Paspalum, Ischaemum, Sphenoclea, Dactyloctenium, Agrostis, Alopecurus, and Apera. -56- In addition, the weeds of the present invention can include, for example, crop plants that are growing in an undesired location. For example, a volunteer maize plant that is in a field that predominantly comprises soybean plants can be considered a weed, if the maize plant is undesired in the field of soybean plants, 5 The articles "a" and "an" are used herein to refer to one or more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one or more elements. As used herein, the word "comprising," or variations such as "comprises" or "comprising," will be understood to imply the inclusion of a stated element integer or 10 step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The following examples are offered by way of illustration and not by way of limitation. 15 EXAMPLE 1: Mutagenesis of Helianthus annuus Line BTK47 and Selection of Imidazolinone-Resistant Plants BTK47, a Helianthus annuus L. breeding line, was chemically mutated as follows. Sixty thousand seeds of the BTK47 line were treated with a solution of ethyl 20 methanesulfonate (EMS) for 15 hours. The treated seeds were then sown under field conditions on December 16, 2002 at Nidera Experimental Station in Venado Tuerto, Santa Fe, Argentina. Approximately 30,000 Mi plants flowered and were covered with bags in order to self-pollinate each plant. Each plant was harvested and threshed by hand. On May 10, 2003 at Nidera Experimental Station in Formosa, 20 M 2 seeds from each 25 capitulum were sown under greenhouse conditions. Approximately 590,000 plants were sprayed at V2-V4 stage with imazapyr at a rate of 80 g ai/ha. Eight plants survived the herbicide treatment and were self-pollinated and harvested. M 3 seeds from each of these eight plants were evaluated for their resistance to imazapyr. Out of these eight M3 families, one family (S4897) segregated for herbicide resistance at a ratio of I resistant 30 (i.e., conferring tolerance to commercial rates of imidazolinone herbicides): 2 intermediate (i.e., partially resistant): 1 susceptible. Fully fertile resistant plants were self pollinated and harvested in order to propagate the line S4897. -57- Leaf tissue from the M3 S4897 plants from both the resistant and intermediate classes were used a source of DNA for analysis of the sequence of the AHASLI gene as described in Example 2. 5 EXAMPLE 2: PCR Amplification and Sequencing of Sunflower Polynucleotides Encoding Imidazolinone-Resistant and Wild-Type AHASL1 Proteins The AHASLI gene was PCR amplified from DNA isolated from M 3 S4897 and BTK47 (wild-type) sunflower plants as two overlapping fragments. PCR amplification 10 was accomplished with Hotstart Taq DNA polymerase and associated reagents (Quiagen Inc, Valencia, California, USA; Cat. No. 203205) using standard methods. The PCR primers for the two fragments are set forth in Table 1 and in the Sequence Listing. HA1U409 (SEQ ID NO: 7) is the forward primer for the first fragment and corresponds to base pair 409 of GenBank Accession No. AY124092. HA1L1379 (SEQ ID NO: 8) is 15 the reverse primer for the first fragment and corresponds to base pair 1379 of GenBank Accession No. AY124092. HA1U1313 (SEQ ID NO: 9) is the forward primer for the second fragment and corresponds to base pair 1313 of GenBank Accession No. AY124092. HA1L2131 (SEQ ID NO: 10) is the reverse primer for the second fragment and corresponds to base pair 2131 of GenBank Accession No, AY124092. The primer 20 pair HA1U409-HA1L1379 produced a 970 base pair fragment. The primer pair HA1U1313-HAIL2131 produced an 818 base pair fragment. The resulting PCR products were sequenced to produce the AHASL 1 sequences for S4897 and BTK47. An alignment of these nucleotide sequences and the nucleotide sequence of the Xanthium sp. ALS gene (GenBank Accession No. U16280; SEQ ID NO: 25 5) is provided in Figure 1. The alignment revealed that the AHASLJ gene from S4897 had a single mutation relative to the AHASLI of BTK47. The site of the mutation is indicated by an asterisk in Figure 1. This mutation is a G-to-A transition that corresponds to nucleotide 21 of SEQ ID NO: 1. An alignment of the predicted amino acid sequences of the AHASL1 nucleotide 30 sequences of S4897, BTK47, and Xanthium sp. is provided in Figure 2. Relative to the AHASL1 amino acid sequence of BTK47, the AHASL1 amino acid sequence of S4897 has an alanine-to-threonine substitution at amino acid position 7 (SEQ ID NO: 2). This amino acid position in SEQ ID NO: 2 corresponds to amino acid position 107 in the full length amino acid sequence encoded by the sunflower AHASLI nucleotide sequence of - 58 - GenBank Accession No. AY541451 (SEQ ID NO: 4) and amino acid position 122 in the full-length amino acid sequence encoded by the Arabidopsis thaliana AHASL nucleotide sequence of GenBank Accession No. X51514. 5 Table 1. PCR Primers for Amplifying the Coding Region of the Sunflower AHASLJ Gene Primer Name Primer Sequence CAGACGTGTTGGTGGAAGC HA1U409 (SEQ ID NO: 7) CTGTAACGCGACCTTAATATC HAIL1379 (SEQ ID NO: 8) TGCTGAAATTGGGAAGAATAAG HA1U1313 (SEQ ID NO: 9) TTTCGTTCTGCCATCACCC HA1L2131 (SEQ ID NO: 10) EXAMPLE 3: Production of a Sunflower Line that is Homozygous for the Herbicide 10 Resistance Characteristics of S4897 A sunflower line that is homozygous for the herbicide-resistance trait was produced from S4897 by selfing and screening resistance to imazapyr. This sunflower line and plants thereof were designated as GM40. After confirming the homogeneity of 15 the progeny for herbicide resistance, plants from the GM40 sunflower line were transplanted under greenhouse conditions and self-pollinated for seed production. EXAMPLE 4: Resistance of S4897 to Imazapic 20 In field trials in Argentina, S4897 plants were tested for resistance to imazapic. The resistance to imazapic was clearly superior to the IMISUN-1 (Ala 19 o-to-Val mutation; equivalent position in Arabidopsis thaliana is 205; see Table 4 below). This trial had -59single row plots and was treated on a windy day, so the actual herbicide dose reaching the plants was likely less than was applied. Nevertheless, S4897 displayed a superior tolerance to imazapic than the Ala, 9 o-to-Val, substitution we present no data from this field trial. 5 Plants of S4897 and IMISUN-1 were also subjected to imazapic treatment under greenhouse conditions. The photograph in Figure 5 shows this comparison when the plants were treated with 100 g ai/ha of imazapic. EXAMPLE 5: Summary of Tolerance and AHAS Activity for Sunflower Line S4897 and 10 Other Clearfield@ Varieties of Herbicide-Resistant Sunflower Methods: Sunflower lines S4897, Clearfield@ sunflower varieties A, B, C and a conventional non-Clearfield variety were sprayed with three rates of imazamox (Raptor m ), 100, 200 and 300 gm ai/ha plus 0.5% Sun It II and two rates of imazapyr 15 (ArsenaTm) 160 and 360 gm ai/ha plus 0.5% Sun It II when the plants were at the two to three leaf stage. Ratings were taken at 14 days after application (DAT) for injury. Injury was rated on a scale from 0 to 9 where 0 = no injury to 9= dead plant. Twelve plants were sprayed per herbicide/rate treatment. Statistical analysis was conducted with STATGRAPHICS Plus 5.0 by using ANOVA and LSD procedures. 20 AHAS activity analysis was also conducted by selecting actively growing young leaves from plants that were not sprayed with herbicide at approximately four weeks after planting. Results: After plants were sprayed, it was realized that a height difference between S4897 and other sunflower varieties would have impacted the actual herbicide 25 dose that was delivered. The spray boom height had been calibrated against S4897 and since the other varieties were taller and closer to the boom they would have received a greater dose of herbicide. Rates were recalibrated for the other varieties to determine the approximate dose they would have received. Assessments were made as presented in Table 2 since it was not possible to make a direct rate comparison due to the effect of the 30 height. For example injury scores were compare for S4897 treated imazamox rate 100 gm ai/ha to the other varieties treated at 75 gm ai/ha. The treatment dose of 300 gm ai/ha for line S4897 was equivalent to the treatment of 200 gm ai/ha for the other varieties, which approximately was 300 gm ai/ha. - 60- Table 2. Adjustment due/herbicide dose received Actual dose received (gm ai/ha) Comparison made (gm ai/ha) Herbicide S4897 Other varieties S4897 Other varieties Imazamox 50 75 100 150 100 75 200 300 200 150 300 450 300 300 Imazapyr 160 240 360 540 360 240 5 Line S4897 had significantly less injury across all herbicide treatments (Table 3). In fact very little injury was observed at the highest rate of either imazamox or imazapyr. The other varieties showed increasing injury across herbicide rate as would be expected. Figure 6 shows a comparison of the injury at the 200/150 gm ai/ha for line S4897, Clearfield@ variety A, and the non-Clearfield control. The growing tip of S4897 showed 10 little to no injury whereas Clearfield@ variety A was significantly in juried and had stopped growing. Table 3. Injury data at 14 DAT for three IMISUNI lines and S4897 sprayed with imazamox or imazapyr. 15 Imazamox Imazapyr (gm ai/ha) (gm ai/ha) Lines 100/75 200/150 300 360/240 S4897 0.5 a 0.8 a 0,8 a 0,8 a Clearfield-Sunflower variety A 4.3 c 4.6 c 6.5 d 5,0 c Clearfield-Sunflower variety B 1.9 b 4.8 c 5.3 c 4.3 b Clearfield-Sunflower variety C 1.8 b 2.9 b 4.6 b 4.9 c Conventional non-Clearfield 7.2 d 8.2 d 8.7 e 8.2 d LSD = 0.7 LSD = 0.7 LSD = 0.6 LSD = 0.7 Statistical analysis was conducted with STATGRAPHICS Plus 5.0 Each value is the mean of approximate 12 observation AHAS activity results also showed less inhibition at the higher concentration of imazamox as compared to a Clearfield@ sunflower and conventional non Clearfield - 61 variety (Figure 7). Inhibition by GleanTM was similar across the three sunflower varieties (Figure 8). Feedback was not presented since the parental background of line S4897 was not available. Since both mutations are in the same AHASL1 locus and all tested varieties were homozygous, there is a qualitative difference in the tolerance conferred by the 5 amino acid substitution in the AHASLI protein of S4897. Thus, the same amount of AHAS enzyme with this new substitution (i.e., Alaio 7 -to-Thr) is capable of catalyzing the formation of more product in the presence of herbicide than does AHAS with the Ala 9 o to-Val substitution. This indicates that AHAS the Ala 1 o 7 -to-Thr substitution has superior tolerance to imidazolinone herbicides than AHAS with the Alaio-to-Val substitution. 10 EXAMPLE 6: Herbicide-Resistant Sunflower AHASL Proteins The present invention discloses both the nucleotide and amino acid sequences for wild-type and herbicide-resistant sunflower AHASL polypeptides. Plants comprising 15 herbicide-resistant AHASL polypeptides have been previously identified, and a number of conserved regions of AHASL polypeptides that are the sites of amino acid substitutions that confer herbicide resistance have been described. See, Devine and Eberlein (1997) "Physiological, biochemical and molecular aspects of herbicide resistance based on altered target sites". In: Herbicide Activity: Toxicology, Biochemistry and 20 Molecular Biology, Roe et al. (eds.), pp. 159-185, IOS Press, Amsterdam; and Devine and Shukla, (2000) Crop Protection 19:881-889. Using the AHASL sequences of the invention and methods known to those of ordinary skill in art, one can produce additional polynucleotides encoding herbicide resistant AHASL polypeptides having one, two, three, or more amino acid substitutions at 25 the identified sites in these conserved regions. Table 4 provides the conserved regions of AHASL proteins, the amino acid substitutions known to confer herbicide resistance within these conserved regions, and the corresponding amino acids in the sunflower AHASLI protein set forth in SEQ ID NO: 4. -62- Table 4. Mutations in conserved regions of AHASLI polypeptides known to confer herbicide-resistance and their equivalent position in sunflower AHASL1 Conserved region' Mutation 2 Reference Amino acid position in sunflower Ala1 22 to Thr Bernasconi et al.A VFAYPGGASMEIHQALTRS3 Alaio 7 Wright & Penner' 4 Pro,97 to Ala Boutsalis et al 7 Pro, 97 to Thr Guttieri et al.' Pro, 9 7 to His Guttieri et al.

9 Guttieri et al.

8 Pro, 97 to Leu AITGQV JRRMIGT 4 Kolkman et al.1 5 Prois2 Proi 97 to Arg Guttieri et al.' Pro1 97 to Ile Boutsalis et al. Pro, 9 7 to Gin Guttieri et al.8 Proisy to Ser Guttieri et al.' Ala 20 5 to Asp Hartnett et al.' i

AFQETP

4 Simpson Alai 90 Ala 2 0s to Val Kolkman et al.1 5 White et al. 6

QWED

4 Trps 7 4 to Leu Boutsalis et al.

7 Trpss 9 Devine & Ser 65 to Asn Eberlein1 3

IPSGG

5 Ala 6 3 g - Sers 53 to Thr Chang & Ser 6 s 3 to Phe Duggleby 7 'Conserved regions from Devine and Eberlein (1997) "Physiological, biochemical 5 and molecular aspects of herbicide resistance based on altered target sites". In: Herbicide - 63 - Activity: Toxicology, Biochemistry and Molecular Biology, Roe et al. (eds.), pp. 159-185, IOS Press, Amsterdam and Devine and Shukla, (2000) Crop Protection 19:881-889. 2 Amino acid numbering corresponds to the amino acid sequence of the Arabidopsis thaliana AHASLI polypeptide. 5 3 The sunflower AHASLI amino acid sequences set forth in SEQ ID NOS: 2 and 4 are not full length and begin with the amino acid sequences FAYPGGASMEIHQALTRS and FAYPGGTSMEIHQALTRS, respectively. 4 The sunflower AHASL amino acid sequences set forth in SEQ ID NOS: 2 and 4 possess this conserved region. 10 'The region of the sunflower AHASLI (GenBank Accession No. AY541451) corresponding to this conserved region has the sequence IPAGG. 'Bernasconi et al. (1995) J. Biol. Chem. 270(29):17381-17385. 7 Boutsalis et al. (1999) Pestic. Sci. 55:507-516. sGuttieri et al. (1995) Weed Sci. 43:143-178. 15 9 Guttieri et al. (1992) Weed Sci. 40:670-678.

'

0 Hartnett et al. (1990) "Herbicide-resistant plants carrying mutated acetolactate synthase genes," In: Managing Resistance to Agrochemicals: Fundamental Research to Practical Strategies, Green et al. (eds.), American Chemical Soc. Symp., Series No. 421, Washington, DC, USA 20 "Simpson (1998) Down to Earth 53(1):26-35. "Bruniard (2001) Inheritance of imidazolinone resistance, characterization of cross-resistance pattern, and identification of molecular markers in sunflower (Helianthus annuus L.). Ph.D. Thesis, North Dakota State University, Fargo, ND, USA, pp 1-78. 3 Devine and Eberlein (1997) "Physiological, biochemical and molecular aspects 25 of herbicide resistance based on altered target sites". In: Herbicide Activity: Toxicology, Biochemistry andMolecular Biology, Roe et al. (eds.), pp. 159-185, IOS Press, Amsterdam 1 4 Wright and Penner (1998) Theor. Appl. Genet. 96:612-620. 1 5 Kolkman et al. (2004) Theor. Appl. Genet. 109: 1147-1159. 30 1 6 White et al. (2003) Weed Sci. 51:845-853. 1 7 Chang and Duggleby (1998) Biochem J. 333:765-777. - 64 - EXAMPLE 7: Production of a GM1606 Sunflower Line A second herbicide-resistant sunflower line was produced by the mutagenesis of sunflower seeds that are wild-type with respect to herbicide resistant by a method 5 essentially as described above in Example 1. The new line and plants of that line are referred to herein as GM1606. The GM1606 sunflower line comprises the same mutation in the AHASLI gene as in the S4897 sunflower line. This mutation in GM1606 is a G-to A transition that corresponds to nucleotide 21 of SEQ ID NO: 1. Such a mutation gives rise an alanine-to-threonine substitution at amino acid position 7 (SEQ ID NO: 2). This 10 amino acid position in SEQ ID NO: 2 corresponds to amino acid position 107 in the full length amino acid sequence encoded by the sunflower AHASL1 nucleotide sequence of GenBank Accession No. AY541451 (SEQ ID NO: 4) and amino acid position 122 in the full-length amino acid sequence encoded by the Arabidopsis thaliana AHASL nucleotide sequence of GenBank Accession No. X51514. 15 EXAMPLE 8: Response of Mutant Events A122T and A205V to Imazapir A greenhouse study was conducted to quantify and contrast the imazapir sensivity of the mutants A122T and A205V in different genetic backgrounds at the whole plant 20 level in sunflower. Seeds of the different sunflower lines that were used in this study were obtained under field conditions. The lines used in the study are listed in Table 5. - 65 - Table 5. Sunflower Materials Hybrid/Line Code Type of Material Mutation Event TH1 Hybrid A205V TH9 Hybrid A205V TH10 Restorer Line A205V GIM 5-7 Manteiner Line A205V IB920 Manteiner Line A205V IR79 Restorer Line A205V TH6 Hybrid A122T TH11 Hybrid A122T TH12 Restorer Line A122T GM40 Manteiner Line A122T GM1606 Manteiner Line A122T GIM 5-6 Restorer Line A122T TH13 Manteiner Line Wild Type Methods 5 Seeds were sown in Petri dishes and, after germination, plantlets were transplanted to pots of 10 cm of diameter in a potting media consisting of equal parts of vermiculite, soil and sand. Plants were grown in a greenhouse under natural light conditions supplemented with 400 W sodium halide lamps to provide a 16 hrs daylength. Day/night temperatures were 25 and 20 *C, respectively. At the V2 stage 10 plants of each 10 genotype were randomly assigned to each treatment consisting of seven imazapir doses (0, 40, 80, 160, 240, 320, 400 and 480 g ai/ha), and a zero-time biomass determination. Experiment was arranged as a randomized block design with a full factorial (sunflower line x treatment) arrangement of treatments and 10 replications. On the day of herbicide application ten plants of each genotype were cut at the 15 cotyledonal node and dried at 60*C for 48 hrs zero-time for dried weight determination. - 66 - The rest of the plants were maintained for 10 days after imazapir treatment (DAT) and their height and root and above ground dry biomass were recorded, Height was determined as the distance between the cotyledonal node and the apex of each plant. For root biomass determination, each plant was taken from the pot and the potting media was 5 washed out from the roots. Above ground biomass data from each line were converted to biomass accumulation after application by subtracting the appropriate average zero-time biomass from each sample. Dry biomass data were converted to percentages of the untreated control plants within each line to allow direct comparisons between groups. 10 Results 1. Height Height of the sunflower lines carrying the A205V mutation did not differ from the untreated controls when a rate of O.5X or IX of imazapir was applied. From 2X to 6X, these lines showed a significant reduction in height which reached 68.9% +/- 3.1 of the 15 untreated controls (Table 6 and Figure 9). In contrast, sunflower lines carrying the A122T mutation showed a lesser height reduction (from 0.6 to 15.8% of the untreated controls for 0.5X and 6X rate of imazapir, respectively). Both groups of lines showed a significative difference between them for their response to an increase in herbicide rate from 2X to 6X (Table 6 and Figure 9). 20 2. Phytotoxicity Index Both mutants showed great differences in their response to the increase in herbicide rate from 0.5X to 6X (Figure 10). Sunflower lines carrying the A122T mutation showed a slightly reduction in leaf size and lighter green color than the control plants as the herbicide rate increase (Table 7). In contrast, plants carrying the A205V 25 mutation did not show any injury at 0.5X or IX of herbicide rate, but the level of injury (yellowish, leaf deformation and leaf necrosis) increased quickly from 2X to 6X (Table 7). Both mutants differed between them significantly for the phytotoxicity index from 2X to 6X (Table 7). 3. Above ground Dty Weight Bionass 30 Dose response curves for dry weight of mutants A122T and A205V are shown in Figure 11. Biomass weight of event A122T was reduced with respect to control plants at 4X, 5X and 6X rates, and this reduction reached 25% for the higher dose, Meanwhile, dry weight of event A205V was reduced with respect to the control plants from 0,5X (40 gai./ha) to 6X. Both mutants showed significant differences between them with respect to - 67 this variable from 0.5X to 6X (Table 8). The same trends were obtained for dry matter accumulation (not shown) but without the confounding effects of the initial differences among genotypes for their zero-time dry weight. 4. Root Biomass 5 As the doses of imazapir increased, root dry biomass of both mutants were reduced with respect to control plants, but the rate of reduction was very different between A122T and A205V (Figure 12). In fact, A205V showed a significant reduction in dry weight root biomass from 12.8% at 0.5X (40 g.a.i/ha) to 75.6% at 6X (Table 9). In contrast, A122T carriers showed a significative decrease in root weight biomass from 3X 10 to 6X, and at the higher dose the reduction reached 38.3% (Table 9). Both mutants showed significant differences between them in their root dry weight response to herbicides rates from 0.5X to 6X (Table 9 and Figure 12). - 68 o - - - - - - 0s JL vi. Q cq f600 04.) 00 C)) 00 48 m--- -- 0 '0 006 d In0 c0) 4-q to'- 0~ 0 01 3 0 C3 0 zD N C C C 4)s 4) do A 0000 4) 9 a CDSO-. CDc Ql id' 0 o o ~ ~ ~ t 4)CCCC-C CC-) 00 o 6 . d C O 'o~ C- , 4) Wi W) 0)a, C,4 CdC bb-- - _R 4) - - - Am 8 1- ) CD % C CO 0O O ) C) C DCI~~ ~ Il Io CC CC C, DC-OU CD4 - -- - qCCC CO % -CO'S i)CC F-4 ' All publications and patent applications mentioned in the specification are indicative of the level of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims. Comprises/comprising and grammatical variations thereof when used in this specification are to be taken to specify the presence of stated features, integers, steps or components or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. 71

Claims (24)

1. A sunflower plant comprising in its genome at least one copy of at least one endogenous gene comprising an acetohydroxyacid synthase large subunit (AHASL) polynucleotide, wherein said AHASL polynucleotide encodes an imidazolinone herbicide tolerant AHASL1 protein comprising the amino acid sequence set forth in SEQ ID NO:2 with another amino acid other than alanine at amino acid position 107 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12, or a variant thereof that further comprises at least one of: (i) an alanine, threonine, histidine, leucine, arginine, isoleucine at amino acid position 182 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12, wherein the protein does not comprise a threonine at amino acid position 107 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12; (ii) a glutamine or serine at amino acid position 182 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12; (iii) an isoleucine or an amino acid other than threonine at amino acid position 188 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12; (iv) an aspartate or valine at amino acid position 190 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12; (v) a leucine at amino acid position 559 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12; or (vi) any one of asparagine, threonine, phenylalanine, or valine at amino acid position 638 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12; wherein said plant is a transgenic or non-transgenic sunflower plant and has increased tolerance to an imidazolinone herbicide as compared to a wild-type sunflower 72 plant, and wherein said AHASL polynucleotide encoding said ASHAL1 protein is not derived from spontaneous mutation.

2. An isolated, recombinant, mutagenized, or synthetic sunflower acetohydroxyacid synthase large subunit (AHASL) polynucleotide, wherein said AHASL polynucleotide encodes an imidazolinone herbicide-tolerant AHASLI protein comprising a threonine or another amino acid other than alanine at amino acid position 107 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12, wherein said AHASL1 protein confers upon a plant increased tolerance to an imidazolinone herbicide as compared to a wild-type variety of said plant.

3. The AHASL polynucleotide of claim 2, wherein said AHASL1 protein comprises: (a) the amino acid sequence set forth in SEQ ID NO:2 with a threonine at amino acid position 107 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12, or a variant thereof that further comprises at least one of: (i) a glutamine or serine at amino acid position 182 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12; (ii) an aspartate or valine at amino acid position 190 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12; (iii) a leucine at amino acid position 559 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12; or (iv) any one of asparagine, threonine, phenylalanine, or valine at amino acid position 638 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12: or (b) the amino acid sequence set forth in SEQ ID NO:2 with another amino acid other than alanine at amino acid position 107 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12, or a variant thereof that further comprises at least one of: 73 (i) an alanine, threonine, histidine, leucine, arginine, isoleucine at amino acid position 182 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12, wherein the protein does not comprise a threonine at amino acid position 107 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO:12; (ii) a glutamine or serine at amino acid position 182 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12; (iii) an isoleucine or an amino acid other than threonine at amino acid position 188 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12; (iv) an aspartate or valine at amino acid position 190 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12; (v) a leucine at amino acid position 559 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12; or (vi) any one of asparagine, threonine, phenylalanine, or valine at amino acid position 638 or an equivalent position relative to the amino acid sequence set forth in SEQ ID NO: 12.

4. An expression cassette comprising a promoter operably linked to the polynucleotide of claim 2 or 3.

5. A method for producing a plant that is tolerant to an imidazolinone herbicide, the method comprising (i) transforming a plant cell with a polynucleotide construct comprising the polynucleotide of claim 2 or 3 operably linked to a promoter that drives expression in a plant cell; and (ii) regenerating the plant from said transformed plant cell.

6. A plant produced by the method of claim 5. 74

7. A method for selecting for a transformed plant cell, the method comprising: (i) transforming a plant cell with a plant transformation vector comprising a promoter and an operably linked polynucleotide according to claim 2 or 3; (ii) exposing said transformed plant cell to an imidazolinone herbicide at a concentration that inhibits the growth of an untransformed plant cell; and (iii) identifying said transformed plant cell by its ability to grow in the presence of said herbicide.

8. A method for controlling weeds in a field, said method comprising (i) growing in the field a plant according to claim 1 or 6; and (ii) contacting said plant and weeds in the field with an effective amount of an imidazolinone herbicide, a sulfonylurea herbicide, a triazolopyrimidine herbicide, a pyrimidinyloxybenzoate herbicide, a sulfonylamino-carbonyltriazolinone herbicide, or mixture thereof to which the plant is tolerant and which would inhibit the growth of a wild-type variety of the plant, thereby controlling the weeds.

9. The method according to any one of claims 5, 7, and 8, wherein said imidazolinone herbicide comprises at least one of: 2-(4-isopropyl-4-methyl-5-oxo-2 imidazolin-2-yl)-nicotinic acid, 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-3 quinolinecarboxylic acid, 5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazol in-2-yl)-nicotin ic acid, 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-5-(methoxymethyl)-nicotinic acid, 2-(4-isopropyl-4-methyl-5-oxo-2-im idazoli n-2-yl)-5-methyl nicotin ic acid, or a mixture of methyl 6-(4-isopropyl-4-methyl-5-oxo-2-i midazol in-2-yl)-m-toluate and methyl 2-(4 isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-p-toluate, or a mixture of any of the foregoing.

10. The method of claim 8, wherein said sulfonylurea herbicide comprises at least one of: chlorsulfuron, metsulfuron methyl, sulfometuron methyl, chlorimuron ethyl, thifensulfuron methyl, tribenuron methyl, bensulfuron methyl, nicosulfuron, ethametsulfuron methyl, rimsulfuron, triflusulfuron methyl, triasulfuron, primisulfuron methyl, cinosulfuron, amidosulfuron, flazasulfuron, imazosulfuron, pyrazosulfuron ethyl, or halosulfuron, or a mixture of any of the foregoing. 75

11. An organ, tissue or cell of the plant of claim 1 or 6.

12. The organ of claim 11, wherein the organ comprises at least one of a stem, a leaf, a root, an inflorescence, a flower, a floret, a fruit, a pedicle, a peduncle, a stamen, an anther, a stigma, a style, an ovary, a petal, a sepal, a carpel, a root tip, a root hair, a leaf hair, a seed hair, a pollen grain, or a microspore.

13. The tissue of claim 11, wherein the tissue comprises at least one of a cotyledon, a hypocotyl, an epicotyl, xylem, hloem, parenchyma, or endosperm.

14. The cell of claim 11, wherein the cell comprises at least one of a companion cell or a guard cell.

15. A seed of the plant of claim 1 or 6.

16. The seed of claim 15, wherein said seed is treated with an effective amount of an AHAS-inhibiting herbicide.

17. The seed of claim 16, wherein said AHAS-inhibiting herbicide comprises at least one imidazolinone herbicide, sulfonylurea herbicide, triazolopyrimidine herbicide, or sulfonylamino-carbonyltriazolinone herbicide, or mixtures of any of the foregoing.

18. The seed of claim 16, wherein said AHAS-inhibiting herbicide is an imidazolinone herbicide.

19. A method for treating seeds, the method comprising treating the seed of claim 15 with an effective amount of an AHAS-inhibiting herbicide.

20. The method of claim 19, wherein said AHAS-inhibiting herbicide comprises at least one imidazolinone herbicide, sulfonylurea herbicide, triazolopyrimidine herbicide, or sulfonylamino-carbonyltriazolinone herbicide, or mixtures of any of the foregoing.

21. The method of claim 19, wherein said AHAS-inhibiting herbicide is an imidazolinone herbicide.

22. A method for genotyping a plant according to claim 1 or 6 or a seed according to claim 15, said method comprising: 76 (i) obtaining genomic DNA from a plant or seed; (ii) using said DNA as a template for a polymerase chain reaction (PCR) amplification comprising a forward AHASL1 primer comprising the sequence set forth as SEQ ID NO:7 and a reverse AHASLI primer comprising the sequence set forth as SEQ ID NO:8; and (iii) sequencing the products of said PCR amplification.

23. A polynucleotide primer when used as an AHASLI primer in the method according to claim 22, comprising the sequence of any one of SEQ ID NO:7, 8, 9, or 10.

24. The sunflower plant according to claim 1, the isolated, recombinant, mutagenized, or synthetic sunflower AHASL polynucleotide according to claim 2 or 3, the expression cassette of claim 4, the method according to any one of claims 5, 7 to 10, or 19 to 22, the plant according to claim 6, organ, tissue or cell according to claim 11, the organ according to claim 12, the tissue according to claim 13, or the cell according to claim 14, the seed according to any one of claims 15 to 18, or the primer according to claim 23, substantially as hereinbefore described. BASF SE AND NIDERA S.A. WATERMARK PATENT AND TRADE MARKS ATTORNEYS P29812AU01 77