AU2005253642B2 - Nucleic acid molecules and their use in plant male sterility - Google Patents

Description

1 NUCLEIC ACID MOLECULES AND THEIR USE IN PLANT STERILITY The present invention relates to nucleic acid constructs. More particularly, the invention relates to constructs comprising genes involved in pollen formation and 5 genetic methods for producing male sterile plants using such constructs. The invention further relates to transgenic plants transformed by the constructs and a male sterility system comprising the constructs. BACKGROUND OF THE INVENTION 10 Heterosis is the term used to describe the superior performance of F1 hybrids over parental ines from which the F1 is derived. In crop plants heterosis often manifests in the production of larger plants, tolerance to stress, disease resistance, uniformity and improved yield, which are collectively referred to as hybrid vigour. 15 Heterosis has been observed and documented in many important crop species and the development of hybrids by plant breeders is established practice. However, hybrids can only be used in crops when effective and economical means of pollination control exist to ensure cross pollination and prevent self-pollination. Pollination control 20 mechanisms include mechanical, chemical and genetic means. A mechanical means for hybrid plant production can be used if the plant of interest has spatially separate male and female flowers or separate male and female plants. For example, a maize plant has pollen-producing male flowers in an inflorescence at the 25 apex of the plant, and female flowers in the axiles of leaves along the stem. Outcrossing of maize is assured by mechanically detasseling the female parent to prevent selling. Even though detasseling is currently used in hybrid seed production for plants such as maize, the process is labor-intensive and costly, both in terms of the actual detasseling cost and yield loss as a result of detasseling the female parent. 30 Further, most major crop plants have both functional male and female organs within the same flower, and therefore emasculation is not a simple procedure. While it is possible to remove by hand the pollen forming organs before pollen is shed, this form of hybrid production is extremely labor intensive and expensive. 35 Chemical means of producing hybrid plants involves the use of chemicals that kill or block viable pollen formation. These chemicals, termed gametocides, are used to 2638457_1 (GHMatters) P49763AU.1 11104/11 2 impart a transitory male-sterility. Commercial production of hybrid plants by use of gametocides is limited by the expense and availability of the chemicals and the reliability and length of action of the applications. A serious limitation of gametocides is that they have phytotoxic effects, the severity of which are dependent on genotype. 5 Other limitations include that these chemicals may not be effective for crops with an extended flowering period because new flowers produced may not be affected. Consequently, repeated application of chemicals is required. Many current commercial hybrid plant production systems for field crops rely on a 10 genetic means of pollination control. In such systems, plants that are used as females either fail to make pollen, fail to shed pollen, or produce pollen that is biochemically unable to effect self-fertilization. Plants that are unable to self-fertilize are said to be "self-incompatible" (SI). Difficulties associated with the use of a self-incompatibility system include availability and propagation of the self-incompatible female line, and 15 stability of the self-compatibility. In some instances, self-incompatibility may be overcome chemically, or immature buds can be pollinated by hand before the biochemical mechanism that blocks pollen is activated. Self-incompatible systems that can be deactivated are often very vulnerable to stressful climatic conditions that break or reduce the effectiveness of the biochemical block to self-pollination. 20 Genetic systems involving cytoplasmic or nuclear genes may be used to generate male sterility. Cytoplasmic male sterility (CMS) is at present the most widely used mechanism of pollen control in crops. However, CMS has a number of disadvantages including increased disease susceptibility, breakdown of sterility under certain 25 conditions, undesirable characters linked to restorer genes (genes that can suppress the male-sterile effect of the cytoplasm and are incorporated into the male parent to restore pollen fertility in the F1 hybrid), unreliable restoration, etc. Crops in which such problems occur are, for example, maize, oilseed rape and wheat. 30 Consequently, plant breeders and seed producers require a versatile and durable male sterility system. The genetic engineering approach has a number of advantages over natural systems. The disruption of the genotype of new male-sterile plants normally associated with the introduction of sterility by sexual means is completely avoided and sterility is not linked to particular cytoplasms as in cytoplasmic male sterility. 35 26384571 (GHMatters) P49763AU.1 11/04/11 3 Nuclear-encoded male sterility (NMS) is caused by mutations in the nuclear genome. The advent of plant genetic engineering technology has now made it feasible to develop strategies to permit the use of NMS genes. 5 Plant breeders and seed producers require a versatile and durable male sterility system. The problems that must be overcome include the isolation of genes that induce male sterility, the production of 100% male-sterile progeny, the achievement of complete female fertility and subsequent restoration of pollen fertility in the F1 hybrid. 10 An aim of the present invention is to determine gene(s) involved in pollen formation and develop methods of preventing pollen formation by disrupting the expression or activity of the gene(s) or their gene product(s). A further aim of the present invention is to develop a method for the production of transgenic male sterile plants and/or seeds and harvest plants and/or seeds so produced. 15 SUMMARY OF THE INVENTION A first aspect provides a nucleic acid construct comprising a nucleic acid molecule encoding AtMYB103 (SEQ ID NO: 22) or encoding an 20 orthologue of AtMYB103 having at least 75% sequence identity to SEQ ID NO: 22, or encoding a variant of AtMYB103 comprising a fragment of at least 150 amino acid residues having at least 85% sequence identity to SEQ ID NO: 22, and a repressor motif. 25 The orthologue may have the sequence provided in SEQ ID NO: 3, SEQ ID NO: 5 or SEQ ID NO: 20. The variant may comprise SEQ ID NO: 18 or up to amino acid residue 168 of SEQ ID No; 18. In one embodiment the repressor motif encodes LDLNLELRISPP (SEQ ID NO: 28) or 30 LDLDLELRLGFA (SEQ ID NO: 27). A second aspect provides a reversible male sterility system comprising a nucleic acid construct comprising a repressor motif fused in frame to the 3' end of a nucleic acid molecule encoding AtMYB103 (SEQ ID NO: 22) or encoding an orthologue of 35 AtMYB103 having at least 75% sequence identity to SEQ ID NO: 22, or encoding a variant of AtMYB1 03 comprising a fragment of at least 150 amino acid residues having at least 85% sequence identity to SEQ ID NO: 22, and a nucleic acid construct 2083739_1 (GHMatters) P49763.AU.1 4 comprising a chimeric molecule encoding AtMYB103 (SEQ ID NO: 22) or encoding an orthologue of AtMYB103 having at least 75% sequence identity to SEQ ID NO: 22, or encoding a variant of AtMYB103 comprising a fragment of at least 150 amino acid residues having at least 85% sequence identity to SEQ ID NO: 22, under the control of 5 a strong anther specific promoter or multiple copies of an MYB1 03 promoter. The methods of the second aspect may utilise the construct of the first aspect. The strong anther specific promoter may be an At39 promoter or a TA39 promoter. 10 The construct of the first aspect may be used to produce a male sterile plant. A third aspect provides a plant cell transformed with the construct of the first aspect. A fourth aspect provides a transgenic plant comprising a plant cell transformed with the 15 construct of the first aspect. A fifth aspect provides progeny of the transgenic plant of the fourth aspect. A sixth aspect provides seeds, tissues, roots, shoots, tubers or propagating material of 20 the transgenic plant of the fourth aspect or the progeny of the fifth aspect comprising the construct of the first aspect. The plant used may be monocotyledonous or dicotyledonous. It may be a legume, crop, cereal, native grass, fruiting plant or flowering plant. It may be a Brassicaceae or 25 other Solanaceae species, including potato and cole vegetables, cabbage, kale, collards, turnips, rutabaga, kohlrabi, Brussels sprouts, broccoli and cauliflower, mustards and oilseeds, crucifers, canola, tomato, grain legumes, wheat, barley, maize, tobacco and rice. 30 The construct of the first aspect comprises a dominant repression motif, for example the motif LXLXLX (the EAR motif described by Hiratsu et al., 2003 Plant J. 35, 177 192). The construct may comprise a MYB1 03 gene, or more than one copy of the, or each, 35 gene. The construct may further comprise one or more additional genes involved in male specific development, such as the AtMYB103 gene shown in Figure 12 (SEQ ID NO. 23). 2683739_1 (GHMattm) P49763AU.I 5 Reversible male sterility is critical for the production of hybrid plant varieties that exhibit a higher yield than either of the parents. In particular the present invention enables regulation of plant genes by turning off the endogenous gene encoding MYB 103 in a female parental line but turning on the endogenous equivalent of a the gene on the 5 hybrid that results from crossing the female parental line with another line. 2083739_1 (GHMattm) P49763 AU I 6 BRIEF DESCRIPTION OF THE FIGURES Figure 1 provides the nucleic acid sequence and proposed amino acid sequence of BnMYB32. 5 Figure 2 provides the nucleic acid sequence and proposed amino acid sequence of BnMYBI03-1. Conserved amino acids are indicated by underscore. Figure 3 provides the nucleic acid sequence and proposed amino acid sequence of 10 BnMYBI03-2. Figure 4 provides the nucleic acid sequence and proposed amino acid sequence of AtMYB32. No known plant transcription elements were identified in the promoter region of AtMYB32. The Bbsl sites are shown underlined, as is the putative TATA consensus 15 sequence. The conserved amino acid sequences found in the carboxyl region of other plant MYB-related proteins are shown underlined. Figures 5a - 5b provide the proposed amino acid sequences of (a) TmH27 and (b)GhMYB9. 20 Figure 6 provides the proposed amino acid sequence of OsMYB1 03. Figures 7a-7d provide the proposed amino acid sequence of (a) ZmMYB32-1, (b) ZmMYB32-2, (c) HvMYB32 and (d) TaMYB32. 25 Figure 8 illustrates a species tree generated from a list of potential BnMYB103-1 orthologues derived from an orthologue search of the NCBI database. Each species is represented by one or more MYB genes (see Figure 9). 30 Figure 9 illustrates a gene tree of plant MYB genes related to BnMYBI03-1, AtMYB103 and BnMYB103-1 are shown in bold. Figure 10 illustrates AtMYB103 probes used to screen B. napus cDNA (600 bp) and genomic DNA (450bp and 500bp) libraries. 35 2638457_1 (GHMalters) P49763.AU.1 11/0411 7 Figure 11 shows the AtMYB103 and p8.1.1 CLUSTAL X (1.8) sequence alignment. Both sequences contain conserved tryptophan and phenylalanine residues typical of the R2R3 repeat regions of plant MYB genes (indicated by underscore). 5 Figure 12 shows the AtMYB103 and BnMYB103-1 CLUSTAL X (1.8) sequence alignment. Arrow heads indicate conserved intron sites. Figure 13 shows the BnMYBI03-1 amino acid sequence indicating conserved amino acids by underscore. 10 Figure 14 shows the AtMYB103 and BnMYBI03-1 CLUSTAL X (1.8) sequence alignment. Figure 15 shows the 700bp RT PCR product. The arrow indicates 700bp RT PCR 15 product. The large product represents amplification from genomic DNA. Lane 1 AEcORI/HindIll marker Lane 2 700bp RT PCR product (1.5 mM MgCl 2 ) Lane 3 700bp RT PCR product (2.0 mM MgC 2 ) Lane 4 products from Bnapus genomic DNA 20 Lane 5 no DNA Figure 16 shows the AtMYB103 and p700-1 CLUSTAL X (1.8) sequence alignment. Figure 17 shows the 800bp RT PCR product. The arrow indicates 800bp RT PCR 25 product. The large product represents amplification from genomic DNA. Lane 1 AEcORI/Hindlll marker Lane 2 800bp RT PCR product (1.0 mM MgC 2 ) Lane 3 800bp RT PCR product (1.5 mM MgCl 2 ) Lane 4 800bp RT PCR product (2.0 mM MgC 2 ) 30 Figure 18 shows the AtMYB103 and p800-19 CLUSTAL X (1.8) sequence alignment. Figure 19 shows the 950bp RT PCR product. The arrow indicates 950bp RT PCR product. 35 Lane 1 AEcORI/Hindlll marker 26384571 (GHMafters) P49763AU.1 11/04/11 8 Lane 2 950bp RT PCR product (2.0 mM MgCI2) Lane 3 950bp RT PCR product (2.5 mM MgC 2 ) Lane 4 no RNA 5 Figure 20 shows the AtMYB103 and p900-10 CLUSTAL X (1.8) sequence alignment. Figure 21 shows the AtMYB103, BnMYBI03-1, p700-1 (SEQ ID NO. 24), p800-19 (SEQ ID NO. 25) and p900-10 (SEQ ID NO. 26) CLUSTAL X (1.8) multiple sequence alignment. All sequences contain conserved tryptophan and phenylalanine residues 10 typical of the R2R3 repeat regions in plant MYB genes (indicated by underscore). Differences in the amino acid sequences are highlighted. Figures 22A-B show A - AtMYB103 promoter - gusA in A. thaliana (Bar = 15mm). B BnMYBI03-1 promoter - gusA in A. thaliana (Bar = 25mm). 15 Figures 23A-B show sections of GUS stained anthers from A. thaliana. A shows anthers from a plant carrying an AtMYB103 promoter-gus A construct (Bar = 20pm). B shows anthers from a plant carrying a BnMYBI03-1 promoter-gus A construct (Bar = 30pm). GUS staining is confined to the tapetum (t) and microspores (m). 20 Figure 24 illustrates the BnMYBI03-1 fragment used to probe B. napus Northern blot. Figures 25A-B show a Northern blot analysis of B.napus tissues. Panel A shows the results of probing with the 484bp BnMYBI03-1 gene specific probe. Panel B shows the 25 results of probing with the ubiquitin probe. Lane 1 dehiscing anthers Lane 2 anthers from flower buds 2-6 mm Lane 3 flower buds 0.5-2 mm Lane 4 flower buds 2.5-5 mm 30 Lane 5 flower buds 6-8 mm Lane 6 shoots Lane 7 roots Figure 26 RT PCR analysis of B.napus tissues. The top panel shows RT PCR 35 products generated from B. napus tissues using primers specific to BnMYBI03-1, a 2638457_1 (GH~atters) P49763AU.1 11/04/11 9 product of 979bp is expected). The bottom panel B shows RT PCR generated using primers specific to the f-8 tubulin gene (a product of 545bp is expected). Lane 1 molecular weight markers Lane 2 dehiscing anthers 5 Lane 3 anthers from flower buds 2-6 mm Lane 4 flower buds 0.5-2 mm Lane 5 flower buds 2.5-5 mm Lane 6 flower buds 6-8 mm Lane 7 shoots 10 Lane 8 roots Figure 27 shows RT PCR analysis of pre and post anthesis anthers for BnMYBI03-1 mRNA. Lane 1 molecular weight markers 15 Lane 2 post anthesis anthers, primers A5956A1 0 & A2485F04 Lane 3 pre anthesis anthers, primers A5956A1 0 & A2485F04 These primers have amplified a 784bp fragment from B.napus cDNA. Lane 4 post anthesis anthers, primers A5962H02 & Z1346E10 Lane 5 pre anthesis anthers, primers A5962H02 & Z1346E10 20 These primers have amplified a 979bp fragment from B.napus cDNA. Figures 28A-B show TA39 promoter GUS expression. A shows TA39::gusA expression in A. thaliana (Bar = 25 mm). B shows TA39::gusA expression in B. napus (Bar = 2 mm). 25 Figures 29A-B show restriction enzyme digests of BnMYBI03-1 sense and antisense constructs. A & B show sense and antisense BnMYB103-1 constructs cloned into pBluescipt with the TA39 promoter. 30 C shows restriction enzyme digests (Pvull & SnaBI) of two clones, indicating the sense orientation in lane 2 (expect fragments of 2513 bp - vector, 2512 bp & 475 bp) and antisense orientation in lane 3 (expect fragmets of 2513 bp -vector, 2171 bp & 816 bp)2 26384571 (GHMafler) P49763AU.1 11/04/11 10 Figure 30 shows BnMYB103-1 sense and antisense constructs. NOS pro indicates nopaline synthase promoter, NPTII indicates neomycin phosphotransferase il and NOS-ter indictes nopaline synthase terminator/ 5 Figure 31 shows PCR anaylsis of A. thaliana plants transformed with sense and antisense BnMYBI03-1 constructs. Lane 1 molecular weight markers Lanes 2-6 PCR products generated from plants transformed with antisense constructs using primers P30 & P32 (903 bp) 10 Lanes 7-11 PCR products generated from plants transformed with sense constructs using primers P30 & P34 (636 bp). Figure 32a shows scanning electron micrographs of pollen from A.tha/iana wild type and BnMYB103-1 transgenic plants. 15 1 shows wild type pollen grains 2 gives detail showing flattened pollen grains from AS22 3 shows representative field of pollen from AS15 showing abnormal grain shape and positioning of germinal apertures. 20 Figure 32b shows scanning electron micrographs of pollen from A.thaliana BnMYB103 I transgenic plants. These panels show pollen from plants transgenic for the sense construct. 1 representative field of pollen from S1 1 2 representative field of pollen from S20. 25 Figure 33 shows production of a construct. Figure 34 shows production of a further construct. 30 Figure 35 A-H illustrate changes in phenotype in A. thalana. Figure 36 shows the nucleotide sequence of TaMYB32 and the alignment of the deduced amino acid sequences of AtMYB32 and TaMYB32. The MYB domain sequences are marked in bold letters and the identical amino acids are underlined. The 35 gaps introduced for optimal alignment are represented by broken lines. 28384571 (GHMatters) P49763AU.? 11/04/11 Figure 37 shows the putative rice AtMYB103 orthologue, OsMYB103. Sequence was obtained from Genbank. Introns are shown in lower case and amino acid sequence is shown below the nucleotide sequence. In the alignment shaded boxes show the 5 position of primers. Conserved MYB repeats R2 and R3 are underlined. Conserved residues important for protein folding are shown in bold. Note - sections of low homology (between 168 and 306 in the AtMYB103 protein) are not shown. Figure 38 shows an alignment of the deduced amino acid sequences of AtMYB103 10 and TaMYB103 fragments and a partial nucleotide sequence of the wheat TaMYB103 gene. Identical amino acids in the alignment are underlined. Figure 39 shows the structure of repressor (top) and restorer (bottom) constructs. The promoters are represented by the lines and the AtMYB1 03 gene by light shading, and 15 the repression motif by dark shading. Figures 40A-C illustrate the structure of AtMYB103 and shows RT-PCR analysis of AtMYB103 transcript. Figure 40A shows the structure of AtMYB103 in the insertion mutant. Boxes represent exons and lines introns. Filled boxes indicate the region 20 coding for the MYB domain and a triangle the T-DNA insertion site. In Figure 40B the amino acid sequence in frame with AtMYB1 03 sequence at the insertion site is shown and the sequence encoded by the T-DNA underlined. Figure 40C RT-PCR analysis of RNA extracted from the developing florets of wild-type (Col) and the AtMYB103 insertion mutant plants. PCR amplifications of AtMYB103 transcripts were carried out 25 for 32 cycles (a), 34 cycles (b) and 36 cycles (c), respectively. The fi-tubulin transcript was amplified for 24 cycles. Figures 41 a-41 e show silique elongation and pollen morphology of wild-type and insertion mutant plants. (a) shows elongated siliques in a wild-type inflorescence 30 (Columbia) and aborted siliques in a mutant inflorescence. (b) shows Alexander's stainin (Alexander, M.P. (1969) Stain Technol. 44, 117-122) of a wild type anther and (c) a mutant anther. (d) shows scanning electron micrographs of pollen from a wild type plant and (e) from a mutant plant. Scale bar = 10pm. 26384571 (GHMaters} P49763AU.1 11/04111 12 Figures 42a-42q shows sections of anthers from wild-type and insertion mutant plants. A Flower sections of wild-type (a, c, e, g, i, k) and mutant (b, d, f, h, j, I, m) plants were stained with safrinin and anther cross-sections were photographed. Developmental stages were assigned according to Sanders et al. (1999) Sex. Plant Reprod. 11, 297 5 322. (a) and (b) show stage 5, (c) and (d) stage 6, (e) and (f) stage 7, (g) and (h) stage 8, (i) and 0) stage 9, (k) and (1) and (m) stage 12. Transmission electron micrographs of sections of a wild-type anther are shown in (n) and mutant anthers (o, p, q). (n) and (o) stage 6, (p) stage 7 and (q) stage 9. pmc, pollen mother cell; td, tetrad; tp, tapetum; ms, microspore; cms, collapsed microspores; v, vacuole; dms, degenerating 10 microspores; pw, pollen wall; db, debris. Scale bars = 10pm. Figures 43a-43d show Silique elongation and pollen morthology of wild-type and repressor plants. A shows the structures of the repressors and the amino acid sequence at the fusion joint. Introns are represented by filled boxes, exons by empty 15 boxes and promoters by lines. The C terminal sequence of AtMYB103 and EAR sequence are underlined. B shows elongated siliques in a wild-type plant (Columbia) (a) and aborted siliques in a P103/103EAR plant (b). Alexander's staining of a wild type anther (c) and a P103/103EAR anther (d). 20 Figure 44a-44e shows sections of anthers from a repressor line. Flower sections of repressor plants were stained with safrinin and anther sections are shown. (a) stage 5, (b) stage 7, (c) stage 9 (longitudinal section), (d) stage 12 and (e) stage 13. Figure 45 shows RT-PCR analysis of the repressor and endogenous AtMYB1 03 25 transcripts. The RNA samples were extracted from developing florets with closed buds of wild-type plants (lanes 1, 2), repressor lines 1, 2, 3 and 4 (lanes 3 and 4, 5 and 6, 7 and 8, 9 and 10), respectively. RT-PCR amplifications were carried out using primers specific to endogenous AtMYB103 transcript (a), repressor transcript (b) and /?-tubulin transcript (c). The PCR reactions (a, b) were terminated at cycles 31 (lanes 1, 3, 5, 7, 30 9) and 35 (lanes 2, 4, 6, 8, 10). The PCR reactions (c) were stopped at cycles 24 (lanes 1, 3, 5, 7, 9) and 27 (lanes 2, 4, 6, 8, 10). The primers in each reaction were positioned on either side of an intron to identify cDNA products. Figure 46 shows a model for hybrid seed production. A male sterile female line 35 transgenic for P103/103EAR is pollinated with pollen from a male line containing the 26384571 (GHMatters) P49763.AU.1 11/04/11 13 restorer P39/103. The restorer out-competes the repressor in F1 hybrid resulting in the restoration of male fertility. Figure 47 shows RT-PCR analysis of the restorer and endogenous AtMYB1 03 5 transcripts. The RNA samples were extracted from developing florets with closed buds of restorer lines 1, 2, 3, and 4 (lanes 1, 2, 3, 4), respectively. The RNA samples were transcribed using a reverse transcriptase with the exception of the samples in (e) and (f). Endogenous AtMYB103 (a, b) and the restorer (c, d) transcripts were amplified for 28 cycles (b, d) and 32 cycles (a, c). The fi-tubulin (g, h) transcript was amplified for 19 10 cycles (h) and 23 cycles (g). The control samples were subjected to PCR amplification without prior reverse-transcription for 28 cycles (f) and 32 cycles (e). Low levels of genomic restorer products (e, f) were detected. Figures 48a-48c show silique elongation of F1 plants. Male sterile P103/103EAR 15 plants were pollinated with pollen from P39/103 plants and F1 silique elongation was examined. Partial restoration (a) and full restoration (b) of F1 silique elongation and aborted siliques (c) from parental male sterile plants. Figures 49A-B show the potential application of the MYB1 03EAR chimeric repressor in 20 hybrid seed production. A - The inducible activator MYB103EcR and the chimeric repressor MYB103EAR are introduced into a female line together or separately. The male sterility caused by the 103EAR is reversed by the agonist-activated MYB103EcR. The resultant male sterile and homozygous female line is then pollinated by a male line containing a restorer MYB103RST. B - the inducible chimeric repressor 25 MYB103EAREcR is transformed into a female line. Male sterility induced by an ecdysone agonist enables the female line to be pollinated by a male line. No restorer is required. DETAILED DESCRIPTION OF THE INVENTION 30 The present invention relates to the identification by the inventors of certain genes which are expressed in the anthers of plants during pollen formation and their work showing that such genes are vital for pollen formation and thus may be blocked to produce male sterile plants. 35 2638457_1 (GHMatters) P49763.AU.1 11/04/11 14 The inventors' earlier research papers, Li et al., Plant Cell Physiol. 40(3); 343-347 (1999) and Higginson at al, The Plant Journal (2003) 35, 177-192 describe a MYB-like gene from Arabidopsis, AtMYB103. This gene was shown to be expressed in the anther during the early stages of anther development and was suggested to be 5 involved in pollen formation. Unpublished work by the inventors showed that blocking of this gene alone in Arabidopsis was insufficient to produce 100% male sterility. Without 100% male sterility pollen is still able to be produced and accordingly heterosis may not be achieved. 10 Subsequent work described in this specification shows the discovery of an additional Arabidopsis gene expressed in anther tissue and involved in pollen formation. Provided herein is evidence that blocking the expression of both the Arabidopsis genes allows production of 100% male sterile Arabidopsis plants. 15 Additionally the inventors have sought to find if there are functional orthoigues of the Arabidopsis genes in other plant species and here describe several such orthologues and methods of inducing male sterility in crop species such as Brassica by blocking the expression of the endogenous gene corresponding to the orthologues. 20 "Nucleic acid" as used herein refers to an oligonucleotide, polynucleotide, nucleotide and fragments or portions thereof, as well as to peptide nucleic acids (PNA), fragments, portions or antisense molecules thereof, and to DNA or RNA of genomic or synthetic origin which can be single- or double-stranded, and represent the sense or antisense strand. Where nucleicc acid" is used to refer to a specific nucleic acid 25 sequence "nucleic acid" is meant to encompass polynucleotides that encode a polypeptide that is functionally equivalent to the recited polypeptide, e.g., polynucleotides that are degenerate variants, or polynucleotides that encode biologically active variants or fragments of the polypeptide, including polynucleotides having substantial sequence similarity or sequence identity relative to the sequences 30 provided herein. Similarly, "polypeptide" as used herein refers to an oligopeptide, peptide, or protein. Where "polypeptide" is recited herein to refer to an amino acid sequence of a naturally occurring protein molecule, "polypeptide" and like terms are not meant to limit the 35 amino acid sequence to the complete, native amino acid sequence associated with the 2638457_1 (GHMatters) P49763.AU,1 11/04/11 15 recited protein molecule, but instead is meant to also encompass biologically active variants or fragments, including polypeptides having substantial sequence similarity or sequence identify relative to the amino acid sequences provided herein. 5 By "isolated" we mean free from material present in nature in the plant from which the nucleic acid molecule is derived, that is in an environment different from that in which the compound naturally occurs. "Isolated" is meant to include compounds that are within samples that are substantially enriched for the compound of interest and/or in which the compound of interest is partially or substantially purified. 10 The nucleic acid molecules of the present disclosure are expressed in anther tissue during pollen formation. Whilst the nucleic acid molecules are not exclusively expressed in the anther, nor only during pollen development, these molecules are more specific than "house-keeping" genes which are active in all plant cells. The 15 invention does not encompass genes that are not expressed in the anther during pollen development. For the avoidance of any doubt the present invention does not encompass the ZmMYBP2 gene, the NtMYBAS1 gene or the NtMYNAS2 gene. None of the prior art in relation to these genes describes that the gene is expressed in the anther during pollen development. The inventors' studies would tend to suggest that 20 the ZmMYBP2 gene, the NtMYBAS1 gene, and the NtMYNAS2 gene are not expressed in the anther during pollen development. The prior art does not specifically disclose that the AtMYB103 gene is expressed in the anther during pollen development. The inventors have found that it is and have also found that blocking expression of this gene alone is not capable of producing 100% male sterility. 25 Accordingly the present invention does not encompass the AtMYB103 gene, although it does encompass the use of the gene in inducing male sterility. Preferably, the majority of the expression of the nucleic acid molecule during pollen development is in the anther. Such molecules may be considered "anther specific". 30 Anther tissue describes the tissue of the male reproductive organs in a plant, be it fully developed or partially developed. The definition of anther tissue used herein is intended to include all structures making up the anther, that is, the epidermis, endothecium, middle layer and tapetum. 35 26384571 (GHMatters) P49763AU.1 11/04/11 16 The nucleic acid molecules disclosed herein encode proteins belonging to the MYB class of DNA binding transcription factors. MYB (myeloblastosis) genes represent the largest family of transcription factors found in plants with around 180 MYB genes known in the genome of A. tha/iana. The first MYB genes were isolated from avian 5 leukaemia viruses and they have now been described in mice, Drosophila melanogaster, Dictyostelium discoideum, yeast and fungi. It has been estimated that over 5% of the Arabidopsis genome codes for transcription factors. This accounts for approximately 1700 genes of which 180 (10.6%) belong to the MYB family. Maize expresses over 80 MYB genes, it is estimated that petunia has at least 40, rice more 10 than 20 and others have been reported in Antirrhinum, barley, pea, sorghum and the moss Physcomitrella patens. The majority of MYB genes found in plants are of the R2R3 type, although some exceptions have been reported. Genes with a single repeat unit have been found in potato and Arabidopsis. 15 The vertebrate family of MYB transcription factors consists of A-, B- and c-MYB and all three are involved in the regulation of cellular proliferation, differentiation and apoptosis. This is in contrast to the many MYB proteins found in plants, none of which have been found to share a similar function. A study aimed at the functional characterisation of R2R3 MYB genes in Arabidopsis has shown that they are 20 expressed in different organs (seedlings, young and mature leaves, cauline leaves, stem, flower buds, siliques and roots) and in response to a variety of environmental conditions (that is different sucrose/nitrogen regimes, hormone treatments, pathogen attack, different light regimes and cold and drought stress). Plant MYB genes are involved in many functions including the regulation of secondary metabolism, cellular 25 development and signal transduction. A number of MYB genes are expressed in response to plant hormones, biotic and abiotic stress. Most of the plant MYB genes with known function are involved in regulating phenylpropanoid metabolism. 30 A number of MYB genes have been suggested to be involved in the regulation of developmental processes such as shoot morphogenesis (AtMYB13), growth and dorsoventrality of lateral organs (PHANTASTICA) embryogenesis (AtMYBRI & AtMYBR2) and anther development (AtMYB103 [Li et al., 1999 supra). 35 26384571 (GHMatters) P49763AU.1 11/04/11 17 Pollen is the haploid male gametophyte in flowering plants and carries the sperm cells required for fertilisation of the ovules. These tiny grains develop within the anther and are released as the anther matures by a process referred to as dehiscence. 5 Pollen formation requires the expression of temporally and spatially specific genes in the gametophyte and sporophyte. It has been estimated that 20 000 mRNA transcripts are present in the mature pollen of Tradescantia paludosa and maize. It is likely that many more transcripts are produced in the early stages of pollen formation, which reflects the complex nature of this process and the need for regulatory genes. 10 The study of pollen formation over many years has shown significant similarities in a number of plant species. In recent years attention has focussed on Arabidopsis thaliana, a model plant for research due to its compact size, short life cycle and small genome which has now been entirely sequenced. 15 The male haploid phase of development in angiosperms results in the production of pollen, the male gametophyte. Pollen develops within the anther a structure composed of four layers, the epidermis, endothecium, middle layer and tapetum. Within the anther locules, adjacent to the tapetum, lie sporogenous cells from which pollen will 20 develop. The expression of temporally and spatially specific genes in the gametophyte (meiocytes) and sporophyte (tapetum) is required for complete pollen development. Mature pollen grains consist of a vegetative and generative cell (bicellular) or a vegetative cell and two sperm cells (tricellular), surrounded by the intine and exine. A number of common developmental stages have been identified: 25 Sporocenesis Sporogenous cells form meiocytes and these undergo two meiotic divisions (meiosis I & II) resulting in a tetrad of haploid microspores surrounded by a p-1,3-glucan (callose) wall. The pollen wall begins to develop as sporopollenin is deposited, forming the 30 exine. Tapetal cells increase in size, numerous ribosomes are present, the endoplasmic reticulum and Golgi proliferate and the number of secretory vesicles increases. As the callose wall degrades, the tapetum reaches its highest secretory phase and the stage of microgametogenesis development ensues. 2638457_1 (GHMatters) P49763.AU.1 11/04111 18 Microgametogenesis During this stage the free microspores grow rapidly with further deposition of the exine layer. This coincides with sporopollenin synthesis and secretion by the tapetum. The microspores become vacuolated, at first with many small vacuoles, which later fuse to 5 form a single large vacuole. At this stage exine formation is complete, sporopollenin synthesis has ceased, deposition of the intine begins and internal degradation of the tapetum has commenced. Microspore maturation 10 This stage is characterised by an asymmetric mitotic division (mitosis 1) that gives rise to a large vegetative cell and a smaller generative cell. The vegetative cell is involved in further pollen development and later in the formation of the pollen tube. The generative cell will undergo another mitotic division (mitosis 11) to produce two sperm cells. The tapetum ruptures releasing cytoplasmic lipid bodies and elaioplasts that 15 associate with the pollen to form a coat. This coat is involved in interactions at the stigmatic surface enabling hydration and successful germination of the pollen grain. Both A. thaliana and B. napus belong to the 30% of angiosperms that produce mature pollen in a tricellular state, i.e. the generative cell divides before pollen dehiscence. 20 The generative cell in the 70% of angiosperms producing bicellular pollen undergoes a mitotic division following germination on the stigmatic surface. The cytological processes and time frame of pollen development are relatively consistent within angiosperms despite obvious differences in floral morphology, pollen size and pollen shape that distinguish various genera and families. The conserved nature of pollen 25 development suggests that the processes and genes involved are also likely to be conserved. Examples of conserved pollen-specific genes already exist. The gene P2 in Oenothera organensis hybridises to similar transcripts in families representing both monocots and dicots. The pollen specific genes Bcpl and Bnm1 appear to be conserved within the family Brassicacea. 30 "Derivatives" of nucleic acid molecules as defined herein encompass those nucleic acid molecules comprising non-naturally occurring nucleotides or those naturally occurring nucleotides that have been modified by chemical or other means. 2638457_1 (GHMatters) P49763.AU.1 11/04/11 19 "Derivatives" of proteins or peptides as defined herein encompass those proteins or peptides comprising non-naturally occurring amino acids or those naturally occurring amino acids that have been modified by chemical or other means. 5 "Derivatives" as used herein in relation to nucleic acid molecules, proteins and peptides are also intended to encompass single or m Itiple nucleotide or amino acid substitutions, deletions and/or additions as well as parts, fragments, portions, homologues and analogues of the nucleic acid molecule or protein or peptide. 10 Functional derivatives as defined herein encompass n cleic acid molecules, proteins and peptides that are derivatives of the wild type MYB nucleic acid molecules, proteins or peptides but that still retain the wild type function of being expressed in the anther during pollen formation. 15 Wild type as defined herein refers to the MYB gene, protein or peptide as found in nature. "Under normal conditions" as used herein is intended to refer to conditions where the inhibiting nucleic acid molecule is not present, i.e. in a plant cell not transformed with 20 the construct of the first aspect. Complementary as used herein in relation to nucleic acid molecule "complementary" to the B. napus nucleic acid sequence or a region thereof, or a functional derivative thereof, is intended to encompass those sequences that are capable of hybridising 25 under high stringency conditions at 42 degrees centigrade to the nucleic acid molecules disclosed herein. "Stringency" of hybridization reactions is readily deterrinable by one of ordinary skill in the art, and generally is an empirical calculation dependent upon probe length, 30 washing temperature, and salt concentration. In general, longer probes require higher temperatures for proper annealing, while shorter probes need lower temperatures. Hybridization generally depends on the ability of denatured DNA to re-anneal when complementary strands are present in an environment below their melting temperature. The higher the degree of desired homology between the probe and hybridizable 35 sequence, the higher the relative temperature which can be used. As a result, it 26384571 (GHMatters) P49763AU.1 11/04(11 20 follows that higher relative temperatures would tend to make the reaction conditions more stringent, while lower temperatures less so. For additional details and explanation of stringency of hybridization reactions, see Ausubel et al., Current Protocols in Molecular Biology, Wiley Interscience Publishers, (1994) and Sambrook et 5 al., Molecular Cloning, A Laboratory Manual, 2nd Edition (1989) Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY). Reference herein to a "region" of the B. napus nucleic acid molecule encompasses a fragment of the B. napus nucleic acid molecule which is expressed in anther tissue 10 during pollen formation and encodes a functional region of an MYB transcription factor. The present disclosure provides specific nucleic acid molecules BnMYB32, BnMYBI03-1 and BnMYB103-2 which encode MYB transcription factors and are expressed in anthers during pollen formation. 15 The inventors provide evidence herein to show that BnMYBI03-1 is expressed during early pollen development. Experiments performed to ascertain the expression pattern of BnMYB103-1 show that 20 it is expressed most strongly in flower buds 0.5-2.0 mm in length. These bud lengths correlate with specific stages of early pollen development. BnMYB32 is expressed in developing anthers, its expression commencing in immature anthers and peaking in mature anthers, i.e. from the onset of pollen meiosis to a peak 25 at the conclusion of meiosis. BnMYB32 is also weakly expressed in developing lateral roots and in emerging root tips. In very young flowers anther primordia are composed of undifferentiated meristematic cells. These cells form a sporogenous cell mass, which will become distinguishable 30 from the tapetum, middle layer, endothecium and epidermis. Archesporial cells align themselves in the anther and divide mitotically giving rise to the tapetum and meiocytes. 0.5mm bud length 2638457 1 (GHMatters) P49763AU.1 11(04/11 21 At a bud length of 0.5mm the meiocytes undergo meiosis, an event that occurs synchronously in all locules within the bud. A second mitotic division produces a tetrad of microspores that secrete a P(1,3)-glucan (callose) wall. Mutants in which there is premature dissolution of this wall are usually male sterile, indicating the importance of 5 callose deposition to the production of viable pollen. The tapetal cells undergo mitosis without cytokinesis producing tetraploid binucleate cells. 1.0mm bud length At 1mm, meiosis is complete and the new microspores form a tetrad enclosed by a 10 callose wall. The tapetal cells increase in size and volume associated with the proliferation of endoplasmic reticulum and Golgi. Vesicles are present, small vacuoles develop and sporadic lipid bodies are observed. The inner tapetal wall is in contact with the tetrad wall and the tapetum loses its tangential walls. 15 1.5mm bud length In 1.5mm buds a cellulosic primexine develops outside the plasmalemma of young microspores. This provides a matrix for the deposition of sporopollenin, the precursors of which are formed within the microspore cytoplasm and secreted outside the cell between the plasma membrane and callose wall. This process begins the formation of 20 the exine, a structure that gives the mature pollen grain its characteristic sculptured appearance. The callose wall is digested by P(1,3)-glucanase (callase), which is secreted into the locule from the tapetum and releases the microspores. Vacuolation of the microspores is initiated with numerous small vacuoles present. The tapetum secretes fibrillar and small osmiophillic vesicles. 25 2.0mm bud length At a bud length of 2mm the unicellular microspores are characterised by the formation of a single large vacuole in the cytoplasm. Sporopollenin deposition continues until exine formation is complete. The radial cell walls of the tapetum are lost and it has 30 started its final degeneration. Starch granules appear transiently in the tapetal plastids. 2.5mm bud length In 2.5mm buds an important asymmetric mitotic division occurs producing bicellular 35 microspores containing a large vegetative cell and a smaller generative cell. The 26384571 (GHattters) P49763.AU.1 11/04/11 22 tapetal cells continue to secrete nutrients into the locule but the cellular organelles exhibit characteristics of degradation. Many of the important developmental processes are complete by this stage as evidenced by the fact that meiotically dividing meiocytes can be removed from the anther and will continue development in vitro. 5 The fact that BnMYBI03-1, BnMYBI03-2 and BnMYB32 expression is strongest in flower buds 0.5-2.0mm in length has implications for its role in regulating genes expressed during these early stages of pollen development. Various other anther expressed genes have been identified in A. thalana and Brassica sp. Function has not 10 yet been assigned to most of these genes and many other genes involved in this process are likely to be identified in the future. However, genes involved in meiotic division, the synthesis of a variety of compounds found in the pollen wall, functions of the tapetum and associated processes are all required during the period in which BnMYB103-1, BnMYBI03-2 and BnMYB32 are expressed. The regulated expression 15 of these genes will be necessary and transcriptional regulators such as BnMYBI03-1, BnMYBI03-2 and BnMYB32 will play an important role. As well as providing isolated nulciec acid molecules involved in pollen formation in B. napus, the disclosure also provides othologues in other plant species and 20 encompasses homologues. A "homologue" is defined as a nucleic acid molecule sharing the same function as another nucleic acid molecule. Homologues are generally determined by sequence similarity as defined by alignment using algorithms such as that in the Advanced 25 BLAST2 service provides by EMBL. Homologous sequences are generally those with a percentage sequence identity of at least 50% at nucleotide or amino acid level according to BLAST analysis. Similarities of at least 60%, 70%, 80% and 90% that are functionally active are said to be 30 homologous sequences. "Percent (%) sequence identity" with respect to the nucleic acid sequences identified herein is defined as the percentage of nucleotides in a candidate sequence that are identical with the nucleotides in the specific MYB nucleotide sequence, after aligning 35 the sequences and introducing gaps, if necessary, to achieve the maximum percent 2638457_1 (GHMatters) P49763.AU-1 11/0411 23 sequence identity, and not considering any conservative substitutions as part of the sequence identity. Alignment for purposes of determining percent nucleotide sequence identity can be achieved in various ways that are within the skill in the art, for instance, using publicly available computer software such as BLAST, BLAST-2, ALIGN or 5 Megalign (DNASTAR) software. Those skilled in the art can determine appropriate parameters for measuring alignment, including any algorithms needed to achieve maximal alignment over the full length of the sequences being compared. For purposes herein, however, % nucleotide sequence identity values are generated using the WU-BLAST-2 computer program (Altschul et al., Methods in Enzymology 266:460 10 480 (1996)). Most of the WU-BLAST-2 search parameters are set to the default values. Those not set to default values, i.e., the adjustable parameters, are set with the following values: overlap span = 1, overlap fraction = 0.125, word threshold (T) = 11, and scoring matrix = BLOSUM62. For purposes herein, a % nucleotide sequence identity value is determined by dividing (a) the number of matching identical nucleic 15 acid residues between the nucleotide sequence of the MYB gene of interest having a sequence derived from the MYB gene and the comparison nucleotide sequence of interest (i.e., the sequence against which the MYB sequence of interest is being compared which may be a MYB variant) as determined by WU-BLAST-2 by (b) the total number of nucleotides of the MYB gene of interest. 20 Percent nucleic acid sequence identity may also be determined using the sequence comparison program NCBI-BLAST2 (Altschul et al., Nucleic Acids Res. 25:3389-3402 (1997)). The NCBI-BLAST2 sequence comparison program may be downloaded from http://www.ncbi.nlm.nih.gov. NCBI-BLAST2 uses several search parameters, wherein 25 all of those search parameters are set to default values including, for example, unmask = yes, strand = all, expected occurrences = 10, minimum low complexity length = 15/5, multi-pass e-value = 0.01, constant for multi-pass = 25, drop-off for final gapped alignment = 25 and scoring matrix = BLOSUM62. 30 "MYB homologue" or "MYB variant nucleic acid sequence" means a nucleic acid molecule which encodes an active MYB polypeptide as defined below and which has at least about 50% nucleic acid sequence identity with a nucleotide acid sequence encoding a full-length native sequence MYB polypeptide sequence as disclosed herein, or any fragment of a full-length MYB polypeptide sequence as disclosed herein. 35 Ordinarily, a MYB variant polynucleotide will have at least about 75% nucleic acid sequence identity, more preferably at least about 76% nucleic acid sequence identity, more preferably at least about 77% nucleic acid sequence identity, more preferably at 2683739.1 (GHMatters) P40763.AU.1 24 least about 78% nucleic acid sequence identity, more preferably at least about 79% nucleic acid sequence identity, more preferably at least about 80% nucleic acid sequence identity, more preferably at least about 81% nucleic acid sequence identity, more preferably at least about 82% nucleic acid sequence identity, more preferably at 5 least about 83% nucleic acid sequence identity, more preferably at least about 84% nucleic acid sequence identity, more preferably at least about 85% nucleic acid sequence identity, more preferably at least about 86% nucleic acid sequence identity, more preferably at least about 87% nucleic acid sequence identity, more preferably at least about 88% nucleic acid sequence identity, more preferably at least about 89% 10 nucleic acid sequence identity, more preferably at least about 90% nucleic acid sequence identity, more preferably at least about 91% nucleic acid sequence identity, more preferably at least about 92% nucleic acid sequence identity, more preferably at least about 93% nucleic acid sequence identity, more preferably at least about 94% 26837391 (GHMatters) P49763.AU. I 25 nucleic acid sequence identity, more preferably at least about 95% nucleic acid sequence identity, more preferably at least about 96% nucleic acid sequence identity, more preferably at least about 97% nucleic acid sequence identity, more preferably at least about 98% nucleic acid sequence identity and yet more preferably at least about 5 99% nucleic acid sequence identity with the nucleic acid sequence encoding a full length native sequence MYB polypeptide sequence as disclosed herein, or other fragments of a full-length MYB polypeptide sequence as disclosed herein. Variants do not encompass the native nucleotide sequence. 10 Ordinarily, MYB variant polynucleotides are at least about 30 nucleotides in length, often at least about 60 nucleotides in length, more often at least about 90 nucleotides in length, more often at least about 120 nucleotides in length, more often at least about 150 nucleotides in length, more often at least about 180 nucleotides in length, more often at least about 210 nucleotides in length, more often at least about 240 15 nucleotides in length, more often at least about 270 nucleotides in length, more often at least about 300 nucleotides in length, more often at least about 450 nucleotides in length, more often at least about 600 nucleotides in length, more often at least about 900 nucleotides in length, or more. 20 An "orthologue" may be defined as genes or gene products which are derived from a common ancestor and share a common function. Orthologues are generally homologues. A study of collinearity between regions of the A. thaliana and B. napus genomes has 25 shown that genes present as a single copy in Arabidopsis are present in between two to eight copies in B. napus. Southern blot data reveals four hybridising bands in the B. napus genome when probed with AtMYB103. Southern blotting of the B. oleracea and B. rapa genomes with the same probe shows two hybridising bands in each species. This result is consistent with the AACC genome of B. napus and the collinearity data 30 available. It is likely that the four clones obtained in this study represent two genes from each of the parental species that have come together in the B. napus genome. Studies of the A. thaliana and B. napus genomes provide important insights into the relationship between these species. Genes that are orthologous between these 35 species share an average of 87% DNA sequence identity and extensive conservation 26384571 (GHMatters) P49763.AU. 1 11/04/11 26 of marker order has been found. Work done to date suggests that Brassica genomes contain three representations of a basic genome with each representation being extensively collinear with the genome of A. thaliana. 5 A practical example of gene conservation between these species is the senescence specific gene SAG12. This gene which codes for a cysteine protease in A. thaliana was used to probe a B. napus genomic DNA library and resulted in the isolation of two homologues. These genes show between 83-86% nucleotide sequence identity with SAG12. The similarities in gene structure and expression patterns of these genes 10 indicate they are orthologues. The ultimate test of functional homology between the two MYB genes would be the rescue of an AtMYB103 mutant by transformation with BnMYBI03-1. It is highly likely that AtMYB103 and BnMYB103-1 share a common function in the regulation of early 15 pollen development and as such represent orthologues. In this context "heterologous" DNA means that the DNA introduced into the cells is a DNA not naturally occurring in the cells in this form. On the one hand, it may be DNA which does naturally not at all occur in these transformed cells or DNA which, even if it 20 does occur in these cells, is integrated at other genetic positions as exogenous DNA and is therefore situated within another genetic environment. Comparison of the AtMYB103 and BnMYB103-1 sequences show a number of similarities that indicate these two genes are likely to be orthologues. Both genes 25 consist of three exons interrupted by two introns at conserved sites and both have an open reading frame of 960bp coding for a protein of 320aa. There is 90% identity between the two sequences at the nucleotide level and 93% at the amino acid level. Within the R2R3 repeat region there is 99% identity at the amino acid level. In the first 400bp of the non-coding region upstream of the ATG start codon there is 74% identity. 30 In Arabidopsis it has been shown that this 400bp promoter region is responsible for the correct spatial and temporal expression of AtMYB103. Other data support the likelihood that these two genes are orthologues, including promoter gusA experiments where AtMYBI03::gusA and BnMYB103-1::gusA 35 constructs transformed into A. thaliana both show identical staining patterns. GUS 26384571 (GHMatlers) P49763.AU.1 11104111 27 activity is evident in the anthers of flower buds from 0.5-3.0mm long. Cross sections through stained anthers show that GUS activity is confined to the tapetum and developing microspores. We show herein that antisense and sense BnMYBI03-1 constructs under the control of a tapetum-specific promoter (TA39 from tobacco), 5 produce an abnormal pollen phenotype in A. thailana. The abnormalities observed are similar to those seen in B. napus plants transformed with the same constructs, indicating that functional homology exists between these two genes. A search of the literature indicates that this is not an isolated case. Examples exist 10 where antisense and sense technology has been used to down regulate the expression of an endogenous gene in a temporally and spatially specific manner. This has been achieved using an homologous gene from another species under the control of a non-native promoter. The tapetum and microspore expressed Brassica gene Bcpl shows 73% identity to its Arabidopsis homologue. A 0.5kb fragment of the 15 Brassica Bcp1 cDNA was used in an antisense construct under the control of a promoter from a pollen-expressed gene of tomato, LA T52. Transformation of this construct into A. thaliana was found to inhibit expression of the endogenous gene. The results showed that the Brassica Bcp1 antisense cDNA was able to inhibit function of the Arabidopsis Bcp1 homologue in haploid microspores, leading to pollen abortion. 20 During phenylpropanoid biosynthesis the first step is catalysed by phenylalanine ammonia-lyase (PAL), an enzyme active in the tapetum during pollen development. Antisense and sense constructs of PAL cDNA from sweet potato under the control of a tapetum-specific promoter from rice, Osg6B, have been transformed into tobacco. 25 Analysis of anthers from transgenic plants showed a reduction in PAL activity, which was accompanied by a partial male sterility phenotype. Another example involves the use of a genomic DNA fragment for the alternative oxidase gene from A. thaliana. Expression of this gene has been demonstrated in the tapetum and pollen during anther development. An antisense construct of this fragment under the control of the 30 tapetum-specific rice promoter Osg6B was transformed into tobacco. Expression of the alternative oxidase gene in transgenic plants was much lower than in wild type and resulted in partial male sterility. The ultimate test of functional homology between the two MYB genes would be the 35 rescue of an AtMYBI03 mutant by transformation with BnMYBI03-1. It is highly likely 2638457_1 (GHMatters) P49763AU.1 11/04111 28 that AtMYB103 and BnMYBI03-1 share a common function in the regulation of early pollen development and as such represent orthologues. The Advanced BLAST2 and Orthologue Search Service at EMBL was used to find 5 sequences likely to represent orthologues of BnMYBI03-1. Using the BnMYBI03-1 amino acid sequence as the query sequence the highest score of 1449 3.6e-1 4 was obtained for AtMYB103. The other genes shown in this analysis are all recognised MYB genes or described as MYB-like, putative MYBs or putative transcription factors. Further analysis with this service produced a species tree (Figure 8) using the NCBI 10 database and a gene tree (Figure 9) based on the neighbour-joining tree computed By CLUSTALW. The species tree is a phylogenetic tree representing evolutionary relationships between the species under consideration. Genes from several species were represented in this analysis and most grouped along family lines, Lycopersicon esculentum and Petunia hybrid from the Solanaceae, Arabidopsis thaliana and 15 Brassica napus from the Brassicaceae and Oryza sativa, Zea mays, and Hordeum vulgare from the Poaceae. However, the grouping of Antirrhinum majus, Gossypium hirsutum and Pimpinella brachycarpa does not reflect a familial relationship. Unsurprisingly, the moss Physcomitrella patens does not group with any of these flowering plants. The sorting. of genes according to this taxonomic tree groups 20 BnMYB103-1 with thirty-one A. thaliana sequences. Fifteen of these genes are MYBs, including AtMYB103, the others are described as MYB-related or transcription factor like proteins. The inventors have isolated orthologues of the B. napus MYB genes from an A. 25 thaliana cDNA library and these genes have been characterised: AtMYB32 This gene is expressed in developing anthers from the onset of pollen meiosis and expression reaches its peak at the conclusion of meiosis. AtMYB32 is also expressed in developing lateral roots and in emerging root tips. Antisense and 30 cosuppression AtMYB32 transgenic plants exhibit an abnormal pollen phenotype. AtMYB103 Expression studies using a promoter::GUS construct suggest this gene is specifically expressed in developing flowers at a stage where the pollen mother cells separate and undergo meiosis to form a tetrad of microspores. GUS activity is highest 35 during the tetrad stage and was expressed in the tapetum and middle layer of the 26384571 (GHMatters) P49763.AU.1 11/04/11 29 anther and in microspores. The GUS activity results have been confirmed with in situ hybridisation experiments [Li et al., 1999 supra]. As AtMYB32 and AtMYB103-1 are expressed at the time of important processes in the 5 anther and pollen indicates that these genes are likely to be involved in regulating other genes required for pollen development. Thus, the isolation of the BNMYB32 and the BnMYBI03-1 and BnMYB103-2 genes and their homologues and orthologues provides a strategy for pollen-control. The 10 gene BnMYBI03-1 is exclusively active in developing anthers, whereas the gene BnMYB32 is active during lateral root initiation, as well as being expressed (turned on) in a number of tissues of the developing anther, including the tapetum (a tissue providing nutrients for pollen development as well as pollen-wall components and enzymes for microspore release from the enclosing callose wall) and the microspores 15 themselves. Expression of the BnMYB103-1 and BnMYBI03-2 genes and the BnMYB32 gene occurs only during the early stages of pollen development, the genes subsequently becoming "silent". Although the precise functions of the genes are not known, they code for proteins that 20 belong to a family of proteins (MYB-like) that bind to specific DNA sequences. Such MYB-like proteins regulate the activity of other genes. Two MYB-like proteins in maize, for example, control anthocyanin synthesis. The inventors' results indicate that the MYB103 gene(s) and the MYB32 gene regulate genes important in pollen development. 25 Experiments in which antisense MYB103 gene(s) and MYB32 gene constructs were placed under control of the Cauliflower Mosaic Virus 35S promoter and introduced into A. thaliana plants, resulted in plants with defective pollen. 30 The inventors have found that their MYB-like genes, express in the anther during pollen development are conserved between species. Consequently, the antisense approach using the A. thaliana or B. napus genes can be expected to function in crops both closely related and distinct (e.g. wheat). 26384571 (GHMatters) P49763.AU.1 11/0411 30 Moreover, the introduced (sense or antisense) MYB103 gene(s) and MYB32 gene can be genetically engineered so that the genes are expressed at high levels in anthers and the expression can be induced by simple chemical treatment of plants. 5 Thus, sense or anti-sense constructs of the specified gene(s) can be utilized by being integrated into the genome of a number of relevant transformable plant species (e.g. canola, tomato, grain legumes, cereals) with anthers and pollen developed therefrom. The inventors propose that the MYB-like genes of the present disclosure may be used 10 in conjunction with other genes that are involved in male-specific development, such as those encoding putative transcription factors NOZZLE, MS1 and MYC class transcription factor (see for example Sorensen, A-M et al., The Plant Journal (2003) 33, 413-423). The use of such genes is likely to improve the percentage efficiency of the induction of male sterility. 15 "Antisense nucleic acid molecules" as described herein defines sequences that are complementary to the disclosed nucleic acid molecules or part thereof. Such antisense nucleic acid molecules, may bind to the endogenous gene and block prevent expression of the functional gene in a plant cell. Antisense techniques generally use 20 short 10 to 20 oligonucleotide fragments which hybridise to essential parts of the gene thereby blocking its expression. Such essential regions of the gene may include regions within the 5' regulatory region such as enhancer and promoter regions and may also include the transcription start site. 25 By "promoter" is meant a minimal sequence sufficient to direct transcription. "Promoter" is also meant to encompass those promoter elements sufficient for promoter dependent gene expression controllable for cell-type specific, tissue-specific or inducible by external signals or agents; such elements may be located in the 5' or 3' regions of the native gene. 30 A promoter may be constitutive but most preferably is inducible. The construct may contain one or more promoters. Plasmids, phage and vectors are all terms to describe carriers for introducing nucleic 35 acid into cells. There are a number of methods available for introducing foreign nucleic 2638457_1 (GHMatters) P49763.AU.1 11/04/11 31 acid molecules into plant cells and it is not intended that the invention is restricted to any one of these carriers. The most generally used transformation methods include particle bombardment, polyethylene-mediated transformation and microinjection. The particular method chosen to obtain transformed plants containing nuclear genomes 5 with the inserted nucleic acid will depend on the plant species. In practice, any nucleic acid used to transform plant cells will most likely be in the form of a nucleic acid construct. 10 In practice, a construct used to transfect the plant nucleus will generally additionally comprise various control elements. Such control elements may include promoters and optionally a ribosome binding site (RBS), positioned at an appropriate distance upstream of a translation initiation codon to ensure efficient translation initiation. 15 Constructs according to the present invention include those constructs comprising an anther specific promoter and at least one gene coding for an MYB transcription factor, which gene is expressed in the anther during pollen formation. A person skilled in the art will be readily able to determine suitable constructs. For 20 example we provide a construct comprising an AtMYBI03 gene under the control of the TA39 promoter, the AtMYB103 gene being provided in either the sense or antisense direction, i.e. 5'to 3' or 3' to 5'. We also provide a construct comprising the BnMYBI03-1 and BnMYBI03-2 genes lined together, and an AtMYB-32 gene, each gene in either the sense or antisense direction and all genes all under the control of an 25 anther specific promoter, Preferably most or all of the constituents of the construct are operably linked. Due to the homology between the genes in different species the inventors propose that 30 MYB genes from one species may be used in constructs used to transform other species and that species specific genes be used in constructs with orthologues from other species, for use in transforming any plant species. 2638457_1 (GHMatters) P49763AU.1 11/04/11 32 For example a construct comprising BnMYBI03-1 and BnMYBI03-2 genes may also include an AtMYB32 gene and be used to transform Brassica species under the control of an anther specific promoter such as TA39 from tobacco. 5 A preferred construct further comprises GVG, a chimeric transcription factor which binds to and activates the 6UAS promoter in the presence of dexamethasone (see Aoyama, T. and Chua, N.H., The Plant Journal (1997) 11(3), 605-612). The construct may also comprise a selectable marker, for example HPT, encoding hygromycine phosphotransferase, to allow for selection of transgenic plants comprising the 10 construct. A further preferred construct further comprises a NOZZLE, MS1 or MYC gene, or other nucleic acid encoding proteins involved in male-specific development (see for example Sorensen, A-M, et at., supra). 15 The construct may incorporate into the plant nuclear genome through recombination events. An anther specific promoter defines any promoter which targets the construct to the 20 anther in preference to other positions. A number of regulatory sequences from the promoter region of anther or pollen specific genes have been identified using promoter deletion analysis. Minimal promoter regions required for tissue-specific gene expression have been described (Twell et al., 25 (1991) Genes & Development 5: 496-507). The chiA promoter from petunia contains the CCACAAAAA motif (van Tunen et al., (1990) Plant Cell 2: 393-401) while the Bpl9 gene from Canola contains the motif TGACG that is also present in the nos and 35S promoters (Albani et al., (1991) Plant Molecular Biology 16: 501-513. The A9 gene from Arabidopsis contains a TATATATA motif in the promoter region thought to direct 30 tapetum-specific expression (Paul et a., (1992) Plant Molecular Biology 19: 611-622). The 52/56 box TGTGGTTATATA and the 56/59 box TGAAATTGTGA are conserved sequence motifs in the tomato LAT genes (Eyal et al., (1995) Plant Cell 7: 373-384). The pollen-specific a-tubulin gene from Arabidopsis also contains sequences similar to the 56/59 box (Carpenter et al., (1992) Plant Cell 4: 557-571). The AAATGA sequence 35 directs pollen specificity in alfalfa promoters (Wu et a., (1998) Sexual Plant 2638457_1 (GHMatters) P49763,AU.1 11104/11 33 Reproduction 11: 181-182). Sequence similarities among tissue specific promoters are restricted to short sequence motifs. Promoters may share a similar sequence but are also influenced by upstream regulatory elements that influence expression levels (Twell et al., 1991 supra). 5 The tobacco TA39 promoter regulates tissue-specific gene expression in the anther tissue (Goldberg et al., (1993) Plant Cell 5: 1217-1229. This promoter is expressed in the microspheres, connective tissue and most highly in the tapetum during early pollen development. The TA39 promoter is widely used in gene constructs to control the 10 expression of transgenes directed to the tapetum tissue in the anther and is a preferred promoter used in the constructs of the present invention. Another preferred anther specific promoter is the AT anther specific promoter described in our co-pending application entitled "Promoter and Uses Thereof". 15 The anther specific promoter is preferably a constitutive but tissue specific promoter. The construct may further comprise means for controlling when the gene is expressed. Such means include the use of an inducible promoter so that expression of the construct may be achieved at a desired time point. Aoyama, T. and Chua, N.H. The 20 Plant Journal (1997) 11(3), 605-612 describe a chemical induction system for transcription in plants. This system utilises a chimeric transcription factor, GVG, consisting of the DNA-binding domain or the yeast transcriptional factor GAL4, the transactivating domain of the herpes viral protein VP1 6 and the receptor domain of the rat glucocorticoid receptor (GR). The promoter is induced in response to 25 dexamethsone (DEX), a strong synthetic glucocorticoid. Once activated by dexamethasone, GVG can induce the transcription from the chimeric promoter by about 100 fold. This system, and other inducible promoter systems, may be used in the constructs of 30 the present invention. Another means for controlling the time of gene expression involves the use of a dominant repressor system. The construct may contain, optionally in combination with an inducible promoter, a repressor/restorer system (as described below) to allow 35 control of expression of the genes in the construct. 2638457_1 (GH~atters) P49763.AU.1 11/04/M1 34 The present invention provides transformed cells comprising a a construct according to the first aspect of the invention. By means of methods known to the skilled person the transgenic plant cells can be regenerated to whole plants. Thus, the plants obtained by 5 regenerating the transgenic plant cells of the invention are also the subject-matter of the present invention. A further subject-matter of the invention are plants which contain the above-described transgenic plant cells. The transgenic plants may in principle be plants of any desired species as previously defined. 10 The invention also relates to propagation material of the plants of the invention, e.g. fruits, seeds, tubers, root-stocks, seedlings, cuttings etc. The plants cells may be transformed with a first construct comprising one or more MYB genes and then be subsequently transformed with a further construct comprising one 15 or more same or other MYB genes or fragments thereof or another gene involved in male-specific development, it is not necessary that all the genes to be introduced on the cell be provided on the same construct. In other words, rather than transforming the genome with a single construct comprising at least two MYB genes and optionally another gene, the genes may be introduced on separate carriers. 20 When two nucleic acid sequences are used they are preferably introduced together by co-transformation. The disclosure provides method for controlling pollen development in a plant by 25 introducing into the plant means of inhibiting the expression of the endogenous MYB gene expressed in the anther during pollen development. Based on the nucleic acid sequences provides persons skilled in the art would be able to design suitable means to substantially block expression of the endogenous MYB 30 gene. An "endogenous gene" is a gene that is naturally present in a cell. The endogenous MYB gene as used herein describes the MYB gene that would be naturally expressed in a plant cell under normal conditions. 35 2638457,1 (GHMatters) P49763AU.1 11/0411 35 The production of plant cells which lack the expression of one or more endogenous MYB genes may for example be achieved by the expression of a corresponding antisense-RNA, of a sense-RNA for achieving a co-suppression effect or the expression of a correspondingly constructed ribozyme, which specifically cleaves 5 transcripts encoding one of the proteins of the present disclosure, using the nucleic acid molecules disclosed or the AtMYB103 gene. In order to block expression of endogenous MYB1 03 gene(s), antisense-RNA is preferably expressed in plant cells and the technique known as RNA interference 10 (RNAi) is used. (Waterhouse et al., (1998) Proc. NatI. Acad. Sci. USA 95, 13959 13964). In brief canola plants expressing the sense sequence of BnMYB103-1 are crossed with plants expressing the same BnMYB103-1 sequence in antisense orientation. F1 plants 15 exhibited pollen abnormality and some male sterility. The F1 phenotypes were more severe than either parent. It is likely that the sense and antisense transcripts of the BnMYBI03-1 transgenes formed double-stranded RNA molecules leading to the degradation of endogenous BnMYBI03-1 transcript. The RNAi system using double stranded RNAs to block gene expression is widely used. 20 In order to express an antisense-RNA, on the one hand DNA molecules can be used which comprise the MYB gene(s) complete sequence, including possibly existing flanking sequences as well as DNA molecules, which only comprise parts of the coding region. These parts have to be long enough in order to prompt an antisense-effect 25 within the cells. Basically, sequences with a minimum length of 15 bp, preferably with a length of 100-500 bp and for an efficient antisense-inhibition, in particular sequences with a length of more than 500 bp may be used. Generally DNA-molecules are used which are shorter than 5000 bp, preferably sequences with a length of less than 2500 bp. 30 Use may also be made of nucleic acid sequences which are highly homologous, but not completely identical to the sequences of the MYB103 nucleic acid molecules. The minimal homology should be more than about 75%. Preferably, use should be made of sequences with homologies between 95 and 100%. 35 2638457_1 (GHMatters) P49763.AU.1 11/04/11 36 In an embodiment the cells of the invention differ from naturally occurring cells in that they contain a heterologous recombinant DNA molecule encoding an antisense RNA, a ribozyme or a cosuppression RNA. Due to the expression of this heterologous recombinant DNA molecule the expression of the MYB gene(s) is prevented, resulting 5 in lack of production of the MYB transcription factors in the anther. As the MYB genes are implicated in the formation and production of pollen, preventing expression of the MYB nucleic acid molecules provides transgenic plants which do not produce pollen. Sense oligonucleotides may also be used instead or together with antisense 10 oligonulcoetides. Preferably the method comprises the use of a system that controls the expression of the MYB gene(s) and allows expression of the gene(s), and hence the production of pollen, to be turned on and off as desired. 15 In one embodiment the system is an inducible system. The inducible system may involve induction of the GVG promoter in a transgenic plant with dexamethasone or some other inducible systems may be used. It is preferred that the system be inducible so that production of male sterile plants may be reversible. The method of 20 choice would involve the use of a cheap, non-toxic inducer molecule that can be sprayed on plants to activate antisense gene(s) and block pollen development. It is preferred that in the absence of inducer, the transgenic plants will produce normal pollen. 25 Another system for controlling expression of a gene of interest, which may be used in the present invention but may also find utility outside the constraints of the present invention, is a repressor/restorer system. In this system the functioning of an essential gene is repressed using a transcription repressor. 30 Transcription repressors use various repressive motifs to block the transcription of their target genes. One repressor motif suitable for use in plants has the amino acid sequence LDLDLELRLGFA (SEQ ID NO. 27) (Hiratsu, K. et al., (2003) supra. Another suitable repressor for use in plants has the amino acid sequence LDLNLELRISPP (SEQ ID NO. 28)(Jin, H. et al., (2000) EMBO J 15, 6150). These motifs are designated 35 EAR (ERF-associated amphiphilic repression). It would appear that the amino acid 2638457_1 (GHMatters) P49763AU-1 11/04/11 37 sequence LXLXLX (SEQ ID NO: 29) is essential to the repression function of the EAR motif AtMYB103 was chosen to test the inducible repressor system in plants. This gene was 5 a suitable candidate as it is strongly expressed in Arabidopsis and encodes a transcription factor, an essential factor in the development of viable pollen. In the system it was proposed that functioning of the AtMYB1 03 gene could be repressed using a repressor motif, but turned back on (restored) by crossing. 10 The two peptide sequences exhibit nine identical or homologous residues. The repressive motif (LDLDLELRLGFA) (SEQ ID NO. 27) from Arabidopsis was fused to four different transcription factors with resultant loss-of-function phenotypes demonstrating that the motif converts transcription factors into strong dominant repressors. Inspection of AtMYB7 (Li, S.F., Parish, R.W. (1995) Plant J. 8, 963) and 15 AtMYB32 C-terminal sequences identified the repressive sequence LDLNLELRISPP (SEQ ID NO. 30). The strategy is to test the repressor/restorer system proposed by studying if you could convert AtMYB103 into a strong repressor using the motif of twelve amino acids to 20 obtain male sterility. The heterozygous male sterile inbred A containing the chimeric AtMYB1 03 repressor (AtMYB1 03Rep) is crossed with inbred B containing a "restorer" to produce male fertile F1 hybrid seeds. The "restorer" will be AtMYB1 03 gene under the control of the strong anther-specific At39 promoter or multiple copy of the AtMYB1 03 promoter or their equivalents. Higher levels of the AtMYB103 protein 25 (activator) in the hybrid plants will alleviate the repression by AtMYB103Rep protein leading to viable pollen production and seed setting. The repressor/restorer system produces 50% male fertile inbred A seedlings. A selectable marker linked to the repressor will provide a selection to cull the male fertile 30 inbred A seedlings before crossing with inbred B. Alternatively, a simple chemical which can overcome the repression by the AtMYB103Rep may be used to induce seed setting of the male sterile plants to obtain the homozygous inbred A seed. The homozygous and male sterile inbred A plants will then be crossed with inbred B plants to obtain F1 hybrid seed. 35 2638457_1 (GHMatters) P49763.AU.1 11/04/11 38 The repressor/restorer reversible male sterility system is being successfully tested in Arabidopsis and is suitable for hybrid seed production in any crop plants including canola and wheat. The repressor/restorer system is the preferred system for use controlling gene expression because it potentially avoids the need to spray crops to 5 achieve control of expression. By disrupting pollen formation there is provided a method for providing male sterile plants, that is transgenic plants which do not produce pollen. The ability to bring about male sterility by the directed expression of genes able to inhibit pollen development or 10 the expression of antisense and co-suppression constructs designed to inhibit genes required for pollen formation in a controlled manner is particularly important. To allow male sterility to be achieved it is important that pollen formation is completely disrupted rather than being merely produced. Blocking one or more of the MYB103 15 may provide complete disruption of pollen formation and hence produces 100% male sterile plants. The percentage efficiency of blocking may be improved if, in addition to MYB103, other genes involved in male-specific development are also blocked. In Brassica napus blocking expression of the BnMYBI03-1 gene alone does not give 20 100% male sterile plants, It is also necessary to block BnMYB32 and probably also BnMYBI03-2. It may also be necessary to block MYC and/or other genes involved in male-specific development (see Sorensen, A-M, et al., supra). In Arabidopsis blocking expression of AtMYB32 and AtMYB103 gives 100% male 25 sterile plants. In Arabidopsis an AtMYB1 03 insertional mutant is provided which exhibits complete male sterility with early tapetum degradation and collapsed pollen. Loss-of-function mutant plants were also obtained using an AtMYB1 03/EAR chimeric repressor. The 30 plants are male sterile and the effects on tapetum and pollen development are similar to those observed in the insertional mutant. The chimeric repressor and restorer constitute a reversible male sterility system which can be adapted for hybrid seed production. This is the first reversible male sterility system targeting a transcription factor essential to pollen development. 35 26384571 (GHMatters) P49763.AU.1 11/04/11 39 It is proposed that because of the extensive homology of the MYB genes of the present invention between species that the sequence used to block expression of an MYB gene in one species could be derived from an MYB gene from anther species. For example a construct comprising the BnMYBI03-1 and BnMYB103-2 genes and the 5 AtMYB32 gene was shown to produce male sterile plants in B. napus. It is proposed that the Brassica and Arabidopsis MYB1 03 genes could be used to produce male sterility in other plant species, including wheat, barley etc. Although such methods may have utility it is especially preferred that the MYB genes 10 used are species specific, particularly to appease any problems perceived in relation to genetically modified organisms. For the purposes of this specification it will be clearly understood that the word "comprising" means "including but not limited to", and that the word "comprises" has a 15 corresponding meaning. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art, in Australia or in 20 any other country. It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The 25 present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Embodiments of the present invention will now be described in the following non limited examples. 30 EXAMPLES EXAMPLE I - Genes from Arabidopsis expressed in the anther during Pollen development 35 a) AtMYB32 2638457_1 (GHMatters) P49763.AU.1 11/04/11 40 Isolation of Genomic Clone An Arabidopsis thaliana (Landsberg erect) genomic library in the vector EMBL3 was screened with a 38-mer oligonucleotide directed against the conserved region of the third repeat of the mammalian MYB DNA-binding domain. 5 Screening procedures were carried out according to Ausubel et al. supra. Hybridisation was performed at 40*C. with the 32 P-labelled 38-mer probe 38mer probe: CCTGGTCGTACTGA(C/T)AA(C/T)GA(AG)ATTAA(A/G)AA(C/T)TA(C/T)TGGAA (SEQ ID NO. 31), followed by washes of 6x SSC at 500C. Positive clones were isolated and subjected to Southern analysis by digesting with restriction enzymes BamHl, EcoRI or 10 Sa/I and probing with the 32 P-labelled 38-mer. A 3.5kb EcoRl-BamHl fragment and a 5.0kb BamH I-Sa/il fragment were isolated and cloned into the vector pTZ18U (Bio-Rad). These clones were further subcloned and sequenced. Plant Transformation 15 The following procedures were principally performed as outlined by Ausubel et al. supra unless otherwise specified. A Bbsl restriction fragment of approximately 1000 bp from the 3.5kb EcoRl-BamHI clone comprising the 5' promoter region of AtMYB32 was blunt ended with T4 DNA Polymerase (Promega) and cloned into the Smal site of pBluescript (Strategene). The 1000 bp 5' promoter fragment in pBluescript was 20 excised with BamHI and EcoRV and cloned into the BamHl and Smal sites of pBl101.3 (Clontech). This construct was transformed into Agrobacterium tumefaciens strain AGL1 using the method outlined by Ditta et al., (1980) PNAS 77: 7347-7351. Agrobacterium harbouring the construct were used to transform Arabidopsis root explants using the methods described by Valvekens et al., (1988) PNAS 85: 5536 25 5540. Transformed cells were selected on a shoot inducing media containing kanamycin (Sigma) 100 pg/mI, and subsequently transferred to a growth medium containing kanamycin at 50 pg/mI. Growth of Plants 30 Transgenic seeds were sown onto plates containing germination media and grown under constant illumination at 220C. for approximately four weeks. Plants were then transferred to hydroponic pots and grown in a nutrient solution under the above conditions. After approximately two weeks, auxin (2,4-Dichlorophenoxy-acetic acid) was added to the pots to a concentration of 25 pM. Plants were harvested and 35 screened for GUS activity as outlined below. 2638457_1 (GHMatters) P49763.AU. 11/0411 41 Polymerase Chain Reaction (PCR) The PCR was carried out according to Klimyuk et al.,(1993) Plant J. 3: 493-494, in which whole plant tissue was subjected to an alkali treatment and used directly in the 5 PCR. A primer pair was generated against regions outside the multi-cloning site of pB101 (Clontech). Primers used were 5'TGTGGAATTGTGAGCGGATA (SEQ ID NO. 32) (725-744 of pB101) and 5'ATTCCACAGTTTTCGCGATC (SEQ ID NO. 33) (929-910 of pBl101). Cycling conditions were 94 0 C. for 30 sec; 58 0 C. for 20 sec; 720C. for 1 min; 36 cycles, followed by a 10 min extension at 72*C. PCR products were 10 visualised on a 2.5% agarose gel. GUS Assays and Histochemistrv Tissues from transformed plants were assayed for GUS activity by incubating overnight at 37CC. in a 0.5 mg/mi X-gluc(5-bromo-4-chloro-3-indoyl-B-D-glucuronide 15 cyclohexylammonium salt) substrate solution. Histochemical analysis was carried out according to Caissard et aL, (1992) Protoplasma 170: 68-76 with samples embedded in LR White resin (London Resin Company). Sections of 10 pm were stained with 1% Saffranin 0 and GUS activity observed under a light microscope. 20 Results AtMYB32 clones were isolated and subjected to Southern analysis. Sequencing indicated that an Arabidopsis myb-like gene had been isolated and this was designated AtMYB32 (Fig. 4). The genomic organisation and amino acid sequence of AtMYB32 were determined through sequence comparison with previously reported plant myb-like 25 genes. The AtMYB32 gene possesses one intron which occurs in the R 3 repeat of the DNA- binding domain. The putative AtMYB32 protein product is comprised of 274 residues with an estimated molecular weight of 31.5 kDa. The N-terminal domain is comprised of the two MYB repeats, (R 2 and R 3 ) and displays high sequence similarity to previously reported plant MYB-related proteins. 30 An Arabidopsis thaliana genomic library was screened with a degenerate 38-mer probe 38mer probe: CCTGGTCGTACTGA(C/T)AA(C/T)GA(A/G)ATTAA(AG)AA(C/T)TA(C/T)TGGAA (SEQ ID NO. 34), directed against a conserved region Three highly conserved tryptophan 35 residues separated by 18-19 amino acids in each of the three c-MYB repeats 2638457_1 (GHMatters) P49763AU.1 11/04/11 42 constitute a hydrophobic core around which three a-helical bundles are positioned in each repeat. Three tryptophan are residues present in the R 2 and two in the R 3 repeat of AtMYB32. 5 As has been found in many plant MYB-related proteins, the first tryptophan in R 3 is substituted by phenylalanine. The binding capacity of c-MYB is not impaired when this tryptophan is exchanged for an aromatic/hydrophobic residue. The carboxyl region of AtMYB32 shows little similarity with other MYB-like proteins except for the sequences GIDPATH, CLDLNLELRISPP and GLNNTRVLDFSTLEMK. A serine-rich region (10 of 10 14 amino acids are serine) occurs within the carboxyl terminus. Expression of the AtMYB32 Promoter-Gus Construct To elucidate the expression pattern of AtMYB32, the 5' promoter region was fused to the GUS reporter gene and used to transform Arabidopsis root explants. Fourteen 15 transformant lines were obtained. To confirm the integrity of the constructs in the transgenic plants, PCR was carried out on plant tissue using primers directed against regions outside the cloning site of the binary vector pB101 (data not shown). GUS activity was initially identified in the anthers during early stages of floral development. Initial GUS expression coincided with stage 9 of Arabidopsis floral development, while 20 maximal GUS levels were observed at floral stage 10. Hence, initial GUS activity coincided with the onset of pollen mother cell meiosis and peaked at the conclusion of the meiotic stage when the microspores were present as tetrads. GUS activity subsequently declined during later stages. This developmental sequence takes approximately 72 hours (based on the estimates of floral development outlined in 25 Bowman J (ed) Arabidopsis an atlas of morphology and development. Springer-Verlag NY (1994)). GUS activity was also observed in emerging lateral roots. GUS activity was associated with the primordia involved in the initiation of lateral roots. As the roots extended, 30 some activity remained in this region and also occurred in the root tip. This is probably because some cells expressing GUS in the primordia are destined to form the tip of the emerging root. Subsequently, GUS activity disappeared. Exogenously applied auxin promotes the formation of lateral roots and recent genetic evidence supports such a role for auxin in vivo. Transgenic lines were grown in hydroponic solution and treated 35 with auxin. After treatment times of between 36 and 48 hours, a substantial increase in 2638457_1 (GHMatters) P49763.AU1 11/04f/1 43 GUS activity was observed throughout the roots, reflecting both the hormone stimulation of lateral root initiation and new staining within the roots (e.g. primary root apices, vascular tissue). No stimulation of GUS activity was detected in the anthers of auxin-treated plants (data not shown). 5 The levels of AtMYB32 expression in both developing anthers and lateral roots appear to be relatively low. Incubation periods of 16-18 hours in X-gluc were needed to obtain adequate staining. However, an 8-10 hour incubation was sufficient to detect activity in auxin-treated roots. Untransformed plants or control transgenic plants transformed 10 with a promoterless GUS construct did not stain (results not shown). Clearly, the presence of AtMYB32 in such divergent tissues as pollen and emerging roots, need not imply that it regulates identical genes in those tissues. Tissue specific MYB partners may be required to form functional transcriptional activators or 15 repressors. b) AtMYB103 AtMYB103 was isolated from a genomic library of Arabidopsis as described in Li et al., 20 supra which is incorporated herein in its entirety by reference. The nucleotide sequence of AtMYB103 has been deposited in GenBank under accession number AF048839. The gene was shown to be expressed during the early stages of anther development and it was proposed, amongst other things, that the gene may regulate pollen development. 25 EXAMPLE 2 - Genes from Brassica expressed in the anther during pollen development Materials and methods carried out in relation to Brassica napus are essentially the 30 same as those carried out for Arabidopsis thaliana as described in detail above. a) BnMYB32 Total RNA from young canola flower buds was subjected to RT-PCR amplification using nested primers, Primer sequences: ATGGGAAGGTCTCCTTGCTGTG (SEQ ID 35 NO. 35), TCATTTCATTTCCAAAGTGCTA (SEQ ID NO. 36), 2638457_1 (GHMatters) P49763AU.1 11/04/11 44 designed using the nucleotide sequence of AtMYB32 and a fragment was sequenced. The protein sequence, shown in Figure 1, codes for a peptide with 80% sequence identity with AtMYB32 (97% identity in the MYB domain) and is designated BnMYB32. 5 The expression pattern of BnMYB32 in canola was determined using Northern blot hybridisation as described in relation to AtMYB32, and was found to be similar to that of AtMYB32 in Arabidopsis. Poly A RNA samples were extracted from canola shoots, roots flower buds and anthers of various developmental stages. A 420 bp BnMYB32 fragment coding for the C-terminal was used as a probe in the Northern blot. The 10 BnMYB32 expressed weakly in roots and young shoots. Its expression commenced in immature anthers and peaks in mature anthers. The nucleotide sequence of BnMYB32 is provided in Figure 1. Another clone identified encodes a protein identical to BnMYB32 but with the deletion 15 of the R2 repeat in the MYB domain. The inventors propose that BnMYB32-R3 may be derived from BnMYB32 via alternative splicing of the BnMYB32 mRNA. BnMYB32R3 peptide sequence: 20 MGRSPCCEKDHTNKGAWTKEEDDLIIKLHSLLGNKWSLIATRLPGRTDNEKNYWNT HVKRKLLRGGIDPTTHRPINEAKAPRDSSETRETEDSLVKFLSFSRQLEKKESFGEER NDQKGLICKKERVEYSIVEEKCLDLNLELRISPPWQDQQHHDETKLWFGKEKYMCTA CRFGLGNGKKCSCDNVKCQVEYSSSSSSHSSSDISSSVIGYDFLG (SEQ ID NO. 37) 25 BnMYB32R3 nucleotide sequence: TGATAAGCTTATGGGAAGGTCTCCTTGCTGTGAGAAGGACCACACGAACAAAGGA GCTTGGACTAAAGAAGAAGACGATCTCATCATCAAACTCCATAGCCTCCTTGGAA ACAAATGGTCTCTTATCGCGACGAGATTACCGGGGAGAACAGATAACGAGATCAA GAACTACTGGAATACACACGTAAAGAGGAAGC11 rGAGAGGAGGGATTGATCCC 30 ACGACTCATCGGCCGATCAACGAAGCCAAAGCTCCTCGTGATTCGTCTGAGACTA GAGAGACAGAGGACTCGCTTGTGAAGTTTCTATCTTTCAGTCGTCAACTGGAGAA AAAGGAAAGT1T1GGGGAAGAGAGAAATGATCAGAAAGGACTGATTTGCAAAAAA GAGAGAGTTGAGTATTCGATTGTTGAAGAAAAGTGCTTAGATTTGAATCTTGAGCT TAGAATCAGCCCGCCATGGCAAGACCAACAGCACCATGATGAGACCAAACTTTGG 35 TTTGGGAAAGAGAAGTACATGTGCACTGCATGCCGI1TTGGGTTGGGAAACGGCA AGAAGTGTAGCTGCGATAATGTTAAATGTCAAGTCGAGTACAGTAGTAGCAGCAG 26384571 (GHMatters) P49763.AU,1 11/0411 45 CAGCCATTCTTCAAGCGATATTAGTAGTAGCGTTATTGGTTATGACTTCTTGGGTA (SEQ ID NO. 38) b) BnMYB103-1 5 Wild type Arabidopsis thaliana (Landsberg Erecta ecotype), Agrobacterium tumefaciens (A GLI strain) and the plasmid pRK2013 were supplied by Dr. David Smyth (Department of Genetics and Developmental Biology, Monash University, Melbourne, Australia). 10 Plasmids pGEM*-3Zf (+) cloning and transcription vector. pBluescript*ll SK (amp t ) phagemid vector. 15 pB1101.2 (kanr) plasmid containing a promoter-less GUS cassette in the binary vector pBIN19, used for plant transformation. [Jefferson, 1987 EMBO J. 6: 3901-3907]. pRK2013 (kanr) a helper plasmid for mobilisation of non-self-transmissible plasmids [[Ditta, 1980 supra]. 20 Bacterial strains E. coli strain DH5a (F-, end Al, hsd R1 7 [rk-, nk]. supE44, thi -1, ~, rec Al, gyr A96, rel Al, A [lac/ZYA-arg F] U169 deoR, [80d lac ZAM1 5]). 25 E. coli strain MV1 190 (A[lac-proAB], thi, supE, A[srt-recA] 306:: Tn10 [tet] [F': tra D36, proAB, lacl acZAM15]). Agrobacterium tumefaciens strain AGLI (AGLO recA::bla pTiBo542AT Mop* CbR [Lazo, 1991 Biotechnology 9: 963-967]. 30 Arabidopsis thaliana line Landsberg erecta ecotype (isolated Landsberg, Germany) containing a homozygous recessive mutation, erecta, which confers a more compact phenotype. 35 Oligonucleotides Universal primer - 5' GTAAAACGACGGCCAGT 3' (SEQ ID NO. 39) 2638457_ (GHMtters) P49763.AU.1 11/04111 46 17mer used for sequencing in pGEM and pBluescript vectors. Reverse primer - 5' AACAGCTATGACCATG 3' (SEQ ID NO. 40) 17mer used for sequencing in pGEM and pBluescript vectors. 5 pB1101 forward primer - 5' TGTGGAATTGTGAGCGGATA 3' (SEQ ID NO. 41) 20mer used for sequencing and amplification. pBl101 reverse primer - 5' ATTCCACAGTTTTCGCGATC 3' (SEQ ID NO. 42) 10 20mer 80 base pairs 3' to the multicloning site, used for sequencing and amplification. A5962H02 - 5' GAAAGAAGAAATGGGTCGGA 3' (SEQ ID NO. 43) 20mer situated at the 5' end of AtMYB103 including the ATG start 15 A6004A01 - 5' CAACCACTTCTCCCTTCAGC 3' (SEQ ID NO. 44) 20mer situated 1 50bp upstream of the AtMYBI 03 TGA stop codon. A5956A10 - 5' GGGGGGGTCGACATGGGTCGGATTCCATGTTG 3' (SEQ ID NO. 45) 32mer beginning at the ATG start codon of AtMYB1 03, including a Sal I restriction site. 20 A2485F04 - 5' GGGGAAGCTTTCCTCCTCCTCGTGCGCGGT 3' (SEQ ID NO. 46) 30mer situated 180bp upstream of the AtMYB1 03 TGA stop codon. Z1346E10 - 5' TAAAAATCAAACCATATGAT 3' (SEQ ID NO. 47) 25 20mer situated at 3' end of AtMYB103 including the TGA stop codon. SRK1 - 5' TTAAAGAGAGACGATCGAGAG 3' (SEQ ID NO. 48) 21 mer situated 20bp upstream of the BnMYB1 03-1 ATG start codon. 30 SRK2 - 5' CTATTTGGCGTCCTGGACCT 3' (SEQ ID NO. 49) 20mer situated 176bp downstream of the BnMYB103-1 ATG start codon. SRK7 - 5' CCAATGGGATCCAAAATGAATCA 3' (SEQ ID NO. 50) 23mer situated at the 3' end of BnMYB103-1 including the TGA stop codon. 35 263457_1 (GHMatlers) P49763.AU.1 11/04/11 47 isolation of plasmid DNA: Alkaline-lysis extraction A rapid alkaline extraction method for the isolation of plasmid [Birnboim, 1983 5 Enzymology 100: 243-255]. Alkaline-lysis/PEG preciptation procedure for sequencing Plasmid DNA for sequencing was prepared using the modified "mini" alkaline lysis/PEG preciptation procedure outlined in User Bulletin Number 18 from Perkin 10 Elmer. Appendix A of the PRISM T M Ready Reaction DyeDeoxy T M Terminator Cycle Sequencing kit protocol Rev.A Restriction enzyme digests 0.5 - 1.0pg DNA was digested in a 20pl reaction using 2pl of the required 1OX buffer 15 and 2 - 4 units of the appropriate restriction enzyme. The reaction mix volume was made up to 20pl with deionised water and incubated for 1 - 2 hours at the appropriate temperature. Resolution of DNA fragments 20 Agarose gel electrophoresis was used to resolve DNA fragments. The agarose concentrations ranged from 0.5 - 1.0 % (w/v) agarose, [Maniatis, 1982 Molecular Cloning: A Laboratory Manuel: Cold Spring Harbour, New York]. 25 Isolation and purification of DNA fragments The BRESAcleanTm DNA purification kit was used to purify DNA fragments from agarose gels. Subcloning of DNA fragments 30 Vector DNA was digested with appropriate restriction enzymes as described in section 2.2.3. The restriction enzymes were heat inactivated at 70*C for 15 minutes before treating the lineralised vector with calf intestinal phosphatase (CIP) to remove the 5'phosphate residues. This was achieved by adding 21 of 10 x CIP buffer plus 1.4 units of CIP to the reaction mix and incubating for 20 minutes at 37*C [Maniatis, 1982 35 supra]. To remove contaminating proteins and salts 400tl of WizardTM purification resin was added to the reaction. It was mixed by inversion for 1 minutes and passed 2638457. (GHMatters) P49763AU.1 11/04/11 48 through a Wizard TM minicolumn as per manufactures instructions. 150 - 300ng fragment DNA and 50 - 1O0ng of vector DNA was incubated in the presence of 3 units of T4 DNA ligase and 1 Il of 10 x T4 DNA ligase buffer in a total volume of 10pl at room temperature for 2 - 4 hours (sticky end ligation) or at 15"C overnight (blunt end 5 ligation) [Ausubel, 1994 supra]. Preparation of electrocompetent E. coli cells A single colony of the E. coli strain to be prepared was inoculated into a 5ml overnight culture of 2YT broth (10g yeast extract, 16g trptone, 5g NaCl, per litre, pH 7.0) 10 containing 10mM MgSO4 and grown at 370C. This was diluted into 500ml of 2YT containing 10mM MgSO4 and grown in two one litre flasks with shaking at 37*C. When the optical density at 550nm reached between 0.8 - 1.0 the cultures were cooled on ice for Ihr. The cells were then pelleted by centrifugation at 4*C for 5min. at 5000xG. The supernatant was discarded and the cells resuspended in 10ml of ice cold 15 1mM HEPES, pH 7.0. 200ml of the HEPES was then added and the cells mixed by gentle inversion. This step was repeated and the supernatant discarded. The cells were resuspended in 200ml ice cold 15% (v/v) glycerol and pelleted. Following centrifugation the supernatant was discarded and the cells resuspended in the glycerol remaining in the tube. Aliquots of the cells were frozen in microfuge tubes using liquid 20 nitrogen and stored at -70*C. Electroporation of E. coli cells 1 jM of a ligation reaction or 25ng of plasmid DNA was added to 40RI of thawed eletrocompetent cells and incubated on ice for 1 minute. The cells were then 25 transformed using the Invitrogen Eletroporator il. Cuvettes with a 0.1cm gap were used and the apparatus set to 1.5kV, 5DpF and 150 ohms. Electroporation was performed according to the manufacturers instructions. 200 1 I of SOC broth was added to the transformed cells and incubated at 37*C for 1 hour. The cells were then plated onto appropriate selective media and incubated overnight at 37"C. 30 Screening of plasmid size The colonies to be screened were patched onto appropriate media and grown overnight at 37"C. A sterile toothpick was used to remove and resuspend cells in 40 pl of 10mM Tris-HCI, pH8.0, 100mM NaCl, 10mM EDTA in a microfuge tube. An equal 35 volume of phenol-chloroform-isoamyl alcohol (25:24:1) and 5pil of stop mix was then added. The tubes were vortexed then centrifuged at full speed for two minutes. 2001 2638457-1 (GHMatters) P49763AU.1 11/04111 49 of the aqueous layer was loaded onto an agarose gel for electrophoresis and analysis using a vector-only sample as a marker. Constructs found to be larger that the vector were then further assessed via restriction enzyme analysis. 5 DNA Sequencing Dye terminator cycle sequencing was performed using the ABI Prism,, BigDyeT" Terminator Cycle Sequencing Ready Reaction kit from Perkin-Elmer and template prepared according to the manafacturers instructons. An MJ Research MiniCyclerTM(PTC-150) was used to amplify the extension products with the following 10 parameters, 96*C for 30 seconds, 50*C for 15 seconds and 60*C for 4 minutes. This cycle was repeated twenty five times. The extension products were precipitated, dried under vacuum and sent to the Microbial Biotechnology and Diagnostic Unit at Monash University (Melbourne, Australia) for electrophoresis. 15 The polymerase chain reaction DNA amplification was performed using taq DNA polymerase and the MJ Research MiniCycler " with Hot BonnetM. The reaction mixture contained the following components, taq DNA polymerase reaction buffer (1X), MgCl (ranging from 1.0 2.0mM), dNTP's (200pM each dNTP), primers (10pM each primer), template DNA (5 20 1Ong), taq DNA polymerase (2.5 units) and double distilled water to make the final volume of 20pl. Cycling parameters varied according the size of the fragment to be amplified and Tm of the primers. Extraction of total RNA 25 The method used is a modification of the procedure by [Logemann, 1987 Analytical Biochemistry 163: 16-20] for RNA extraction from plant tissue. One gram of plant tissue was frozen in liquid nitrogen and ground to a fine powder using a mortar and pestle. The powder was transferred to a 15ml tube and 2ml of extraction buffer (8M guanidine hydrochloride, 20mM MES, pH7.O, 20mM EDTA, 50mM mercaptoethanol) 30 added. Three millilitres of phenol/chloroform(phenol/chloroform/iso-amylalcohol, 25:24:1) was added and the tube shaken to extract the nucleic acids. The tube was centrifuged for 10min at 3 OOOxG, the upper phase transferred to a new tube containing 3mi phenol/chloroform and the extraction and centrifugation steps repeated. The upper phase was transferred to another 15ml tube containing 0.2 volumes 1 M 35 acetic acid and 0.7 volumes freezer-cold ethanol. The RNA was allowed to precipitate 26384671 (GHMatters) P49763.AU.1 11/04111 50 at -20*C overnight. The tube was centrifuged for 25min at 9500xG, the supernatant removed and the pellet air dried for 2min. The pellet was then resuspended in 1 ml of DEPC-saturated water, transferred to a 1.5ml microfuge tube and LiCI added to a final concentration of 2M. The tube was mixed and incubated overnight at 4 0 C. The tube 5 was centrifuged for 15min at full speed at 4 0 C. The supernatant was discarded and the pellet resuspended in 500pl DEPC-saturated water. To this was added 50pI 3M Na acetate, pH5.2, and 1000pIl freezer-cold ethanol. This was mixed and incubated overnight at -20"C. The mixture was centrifuged at full speed for 15min at 4"C, the pellet resuspended in DEPC-saturated water at a final concentration of 5pg/ml and 10 stored at -70 0 C. Quantification of total RNA An aliquot of total RNA was diluted 1/1000 in 1X TNE buffer (10X - 100mM Tris base, 10mM EDTA, 2.OM NaCl, pH 7.4) and absorption of the sample measured at different 15 wave lengths to determine concentration and purity. Absorbance at 260nm was used to determine concentration. The ratio of absorbance at 260 and 280nm was used to indicate purity and absorbance at 325nm to indicate contaminating particulate matter. Isolation of polyadenylated RNA 20 Dynabeads* Oligo (dT) 25 were used to isolate polyadenylated RNA from total RNA according to the manufacturers instructions. Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) SuperScript T M 11 Rnase H- reverse transcriptase (Gibco BRL) was used to synthesize 25 first strand cDNA according to the manufacturers instructions using gene specific primers. This first strand cDNA was used in a PCR to amplify the fragment of interest according to the protocol suggested by the manufacturer. Extraction of genomic DNA from Arabidopsis 30 2 - 5g of ground frozen tissue was transferred to a 50ml tube containing 25ml of CTAB extraction buffer. The sample was shaken vigorously and incubated at 65"C for 20 minutes with occasional shaking. 1Oml of chloroform was added to the sample and placed on an inverter for 20 minutes. To resolve the phases, the sample was centrifuged for 5 minutes at 3,000 rpm in a bench top centrifuge. The aqueous phase 35 was transferred into a fresh 50ml tube containing 17ml of isopropanol, mixed, and 2638457_1 (GHMatters) P49763.AU.1 11/04/11 51 incubated on ice for 10 minutes. The sample was centrifuged at 3,000 rpm for 5 minutes and the supernatant was discarded. The precipitate was resuspended in 4ml of TE buffer by gently passing the solution up and down a pipette tip. 4ml of 4 M LiAc was added and the sample was incubated on ice for 20 minutes. The sample was 5 centrifuged for 5 minutes at 3,000 rpm. The supernatant was discarded and the pellet resuspended in 900l of TE buffer. To remove contaminating RNA, 25pjg/ml of RNase was added and incubated at 37 0 C for 5 minutes. 100 I1 of 3M NaOAc was added, mixed, and divided equally into two microfuge tubes. The samples were extracted with 50pOI of buffered phenol (pH 8.0), buffered phenol:chloroform (1:1) and chloroform, the 10 aqueous phase was transferred to a fresh microfuge tube after each extraction. Two volumes of 100% ice cold ethanol was added and the samples incubated on ice for 5 minutes. The DNA precipitate was collected by spinning the samples for 5 minutes at 13,200 rpm at 4CC. The supernatant was discarded, the pellet washed twice with ice cold 70% (v/v) ethanol, dried under vacuum and resuspended in 200pl of sterile 15 deionised water. DNA Quantification DNA was diluted 1/1000 in TEN buffer and absorbance measured at 260nm. The ratio of absorbance at 260 and 280nm was used to indicate purity. 20 Construction of Brassica napus cDNA library A B. napus flower-bud cDNA library was constructed using the ZAP Express* cDNA synthesis kit and ZAP Express* cDNA Gigapackolll Gold cloning kit from Stratagene. Total RNA was extracted from B. napus flower-buds using the protocol outlined above 25 and poly(A)* RNA isolated using Dynabeads. The synthesis of cDNA was carried out using 5pg of poly(A)* RNA and subsequent steps required for construction of the cDNA library were performed according to the instruction manual accompanying the kit (Revision #080012 and #200403-12). Plaque lifts, library screening and in vivo excision were all performed according to the instruction manual. 30 Northern blotting Approximately 3ug of Poly(A)* RNA from each sample was electrophoresed on a 1% agarose gel (50% formamide) with an RNA molecular marker (Promega). The RNA was blotted onto a positively charged nylon membrane (Hybond N, Amersham) using 35 the upward capillary method of transfer [Ausubel, 1994 supra]. The filter was 263457_1 (GHMatters) P49763AU.1 11/04/11 52 prehybridised (5x SSC, 5x Denhardt's, 1% SDS, 50% formamide with 100pg/ml salmon sperm DNA) for two hours at 420C. The probe was labeled with 32 P dCTP (250pCi, Geneworks) using the Megaprime DNA labeling kit (Amersham). Unincorporated nucleotides were removed using a Nickspin column (Amersham). The 5 denatured probe was added to the prehybidisation solution in a glass tube and allowed to hybridise to the filter overnight at 420C with constant rotation in a Hybaid oven. Post hybridisation stringency washes included 2xSSC, 0.1 %SDS at RT for 2x5min; 0.2x SSC, 0.1%SDS, at RT for 2x15min and 0.2xSSC, 0.1%SDS, at 42*C for 2x15min. The filter was then wrapped in plastic and exposed to x-ray film overnight at -70*C in a film 10 cassette. Methods: Plant transformation The plant transformation protocol described below is based on methods devised by Lazo, 1991 supra and modified by C. Johnson, Department of Genetics and 15 Developmental Biology, Monash University, (Melbourne, Australia). Tri-parental mating Fresh liquid cultures of Agrobacterium tumefaciens (AGLI strain), E. coli containing the required binary vector with insert and E. coli containing the plasmid pRK2013, were 20 prepared. A 1 00 il aliquot of each culture was mixed in a tube then plated onto 2YT plates and incubated overnight at 280C. Two streaks of cells were resuspended in 1 OpI of 2YT broth. The resuspended cells were streaked for single colonies on 2YT plates containing 75pg/ml kanamycin and 100gg/ml ampicillin. Several single colonies were inoculated in 2YT broth containing the appropriate antibiotics and grown for 2 25 days at 28*C with vigorous shaking. Plasmid DNA extracted from the culture was used in a PCR with insert specific primers. Presence of the amplified insert indicates that successful tri-parental mating has occurred. Growth and transformation of Arabidopsis thaliana roots 30 Arabidopsis thaliana seeds were surface sterilised in a microfuge tube by washing the seeds with 0.5ml of 70% (v/v) ethanol. The ethanol was removed, replaced with seed sterilising solution (4% chlorine, water, 5% SDS at a ratio of 8:15:1 respectively) and incubated for 10 minutes. The seed sterilising solution was removed and the seeds washed several times in sterile water. Sterilised seeds were sown into 12.5mm petri 26384571 (GHMatters) P49763.AU.1 11/04/11 53 dishes containing 50ml of GM media and sealed with micropore tape. The seedlings were grown at 22 0 C for 2 weeks under constant illumination (80 pEm.

2 s") Roots harvested from Arabidopsis plants were placed parallel onto CIM plates and 5 sealed with micropore tape. The plates were wrapped in foil and incubated at 22*C for 2 days. The roots were cut into 0.5cm pieces, added to liquid cultures of AGLI, shaken and strained through a sterilised steel tea strainer. Excess AGLI was removed by lightly blotting onto sterile 3MM paper and the roots spread over a CIM plate. The plates were sealed with micropore tape, wrapped in foil and incubated for a further 2 10 days at 25 0 C. Roots removed from CIM plates were washed to remove bacteria by vigorous shaking with sterile water in 50ml tubes. A sterile steel tea strainer was used to strain the roots, and they were blotted dry on sterile 3 MM paper. The roots were carefully spread over SIM media containing 1 00pg/ml kanamycin and 200pg/ml timetin, sealed with micropore tape and incubated at 22 0 C under constant illumination (80 FtEm 15 2s~1). Selection of transformants Shoots produced from root cultures were transferred into 150mm pots containing GM media with 50pg/ml kanamycin and 200pig/ml timentin. A small leaf from each shoot 20 was used to check for successful transformation. The leaf was placed into a microfuge tube with 40I of 0.25M NaOH, boiled for 30 seconds and neutralised by adding 40g 1 0.25MHCI and 2Ol1 0.5M Tris-HCI (pH 8.0) containing 0.25% (v/v) Nonident P-40 before boiling for a further 2 minutes. The leaf sample was immediately used for PCR as described above. An amplified PCR product of the desired size indicated that 25 successful transformation had occurred. Transformed shoots containing the insert of interest were grown to maturity Histochemical assay of transformed Arabidopsis plants Seeds generated from plants transformed with pBl101 containing the promoter::gusA 30 construct were surfaced sterilised and sown onto GM plates containing 50 pg/pl kanamycin and grown under constant illumination at 22*C for 2 weeks. Germinated plants that retained their chlorophyll content were transferred to soil. Floral clusters were removed from the plant and placed into a microfuge tube containing X-gluc solution and incubated at 37 0 C for 12 - 15 hours. The chlorophyll was leached from 2638457_1 (GHMatters) P49763.AU.1 11/04/11 54 the plant tissue by placing the tissue into 100 % ethanol. GUS staining was examined under a dissecting microscope. Staining, embedding and sectioning of transformed plants 5 Floral heads were pre-fixed with 1% (v/v) glutaraldehyde made up in 50mM sodium phosphate buffer (pH 7.4) for 5 minutes at room temperature. Tissue was washed 4 times with 50mM sodium phosphate buffer (pH 7.4) for 5 minutes each time. The tissue was covered with X-gluc and incubated overnight at 37 0 C. The tissue was post fixed in a solution of 6% (v/v) glutaraldehyde and 4 % (v/v) paraformaldehyde made up 10 in 50mM sodium phosphate (pH 7.4) and incubated for 2 hours at 40C after 1 minute vacuum infiltration. The tissue was washed three times with 50mM sodium phosphate buffer (pH 7.4) for 5 minutes each time. The floral heads were slowly dehydrated by incubating them for 15 minutes each time with increasing concentrations of ethanol (15%, 50%, 70%, 90% and 100% (v/v)). The tissue was transferred into a fresh tube 15 containing 30% LR white : 70% ethanol (v/v) and incubated at room temperature for one hour. This solution was replaced with 50% LR white: 50% ethanol (v/v) and incubated for a further hour. The tissue was placed in 100% LR white and incubated overnight at 40C. The next day, the tissue samples were placed into plastic boats; covered with 100% LR white; covered to exclude oxygen and incubated overnight at 20 65 0 C. Embedded plant tissue was mounted on a microtome, cut into 10;xm sections and mounted on a clean slide. The sections were stained with 1% (wlv) safranine dye for 2 minutes with gentle heating. Excess dye was washed off with water and then with 50% (vfv) ethanol. Finally the sections were rinsed with 100% ethanol, arranged on the slide and dried with gentle heating. A small drop of clearene and 4 small drops of 25 mounting medium were placed on the sections. The sections were covered with a coverslip and placed on a slide heater. The slide was incubated overnight at 500C with a small weight of 200 grams placed on top. The slides were viewed under the light microscope. 30 Electron microscopy Samples analysed using the scanning electron microscope were critical point dried in liquid C02. The samples were coated with palladium-gold and examined using a JEOL JSM 6340F field emission scanning electron microscope. 26384571 (GHMatters) P49763AU.1 11/04/11 55 Flower buds at various stages of development were embedded in LR White Hard according to Chaudhury et a/. (1994) supra. Sections of 70-90nm were mounted on 50-1 00nm FORMVAR coated copper grids and double stained in uranyl acetate for 6.5 minutes followed by staining in lead citrate for 1.5 minutes. The stained sections were 5 then examined at 80kV in a JEOL 2010 transmission electron microscope. Results Isolation of clone p8.1.1 from a B. napus cDNA library The isolation of an AtMYB103 homologue from B.napus began with the construction of 10 a flower bud cDNA library (see above). Flower buds representing a number of developmental stages, from 0.5mm to the point before flower opening were used for the extraction of RNA. Flower buds of these sizes contain microspores at a variety of developmental stages. These include meiocytes, tetrads and newly released microspores in the smaller buds and binucleate or trinuleate microspores prior to 15 anthesis in the largest buds. The cDNA library was screened using a 600bp probe derived from AtMYB103 including the R3 repeat and part of the C-terminal region, (figure 10). An initial screen of 1x106 plaques led to the isolation of four clones following tertiary screening at high 20 stringency (0.2X SSC, 0.1% SDS, 65*C). These four clones were sequenced and found to be identical. The clone p8.1.1 consists of an ORF 969bp long with a putative amino acid sequence of 323aa. It contains the imperfect R2R3 repeats characteristic of plant MYB genes, 25 including conserved tryptophan residues. However, compared with AtMYB103 it shows an overall identity of 43% at the nucleotide level and 31% identity at the amino acid level (Figure 11). A BLASTN search of the NCBI data base gave the following results. At the nucleotide level the highest identity is with an A. thaliana putative transcription factor, MYB35 (AF062877) with a score of 361 4e-97. This partial 30 sequence contains only 27bp of the R2 repeat but shows significant homology within the repeat region, namely 92%. Portions of significant homology occur at the 3' end of the sequence with an overall identity of 62%. Romero et al. (1998) The Plant J. 14: 273-284 identified MYB35 in a systematic search for R2R3-MYB regulatory genes in the genome of A. thaliana but no functional characterisation has been reported. A 35 phylogenetic tree based on the amino acid sequence outside the R2R3 domain 26384571 (GHMatters) P49753AU.1 11/04/11 56 classifies the MYB proteins into 22 subgroups [Romero, 1998 supra]. However, MYB35 does not fall within any of these subgroups. A BLASTP search showed highest identity with a transcription factor-like protein found on chromosome three of A. thaliana. This protein has a 95.6% identity in the R2R3 region and an overall identity 5 of 75% with the clone p8.1.1. Both the BLASTN and BLASTP searches showed identity to AtMYB103 with scores of 62 5e-07 and 213 1e- 4 respectively. This may be considered significant, however the greatest identity between these sequences is in the conserved R2R3 repeats showing 10 69% identity at the amino acid level. The overall amino acid identity is only 31%, indicating that clone p8.1.1 is unlikely to represent an AtMYB103 homologue. Isolation of an AtMYB103 homologue from a B. napus genomic library A B. napus genomic DNA library (Clonetech FL1 12d) was screened in this laboratory 15 by Roger Kalla (personal communication) with AtMYBI03 3' and 5' probes mixed (Figure 11). The 3' probe was gene specific and excluded the R2R3 repeats. The 5' probe includes 130bp of the R2 repeat and 320bp of the sequence upstream from the ATG start codon. This screening identified two recombinant phage particles containing homologous sequences. Sequence data from these clones show a gene of similar 20 structure to AtMYB103 consisting of three exons interrupted by two introns at conserved sites (Figure 12). An ORF of 960bp coding for a protein of 320aa similar to that of AtMYB103 was identified (Figure 13). This clone, BnMYBI03-1, shows 93% identity to AtMYBI03 at the amino acid level, with 99% identity in the R2R3 region and 89% identity in the putative activation domain (Figure 14). A BLASTP search showed 25 the highest score of 561 e5 with AtMYB103. Isolation of clones p700-1, p800-19 and p900-10 using the reverse transcriptase polymerase chain reaction RT PCR was used in an attempt to isolate an AtMYB103 homologue. First strand 30 cDNA derived from the polyA* RNA of immature B.napus flowers was used as template in a reaction with AtMYB103 specific primers. A 700bp product was obtained as a result of two rounds of amplification using nested primers. The first reaction used primers A5962H02 and A6004A01 situated at the 5' start site and putative 3' stop site of the AtMYB103 sequence respectively. (Subsequent analysis of the 3' region of 35 AtMYB103 has placed the stop codon further downstream). A set of nested primers, 2638457_1 (GHMatters) P49763.AU.1 111/04/11 57 A5956A1 0 and A2485F04 were then used to ensure specificity of the amplified product (Figure 15). The 700bp product was cloned as a blunt ended fragment into the Sma I site of pBluescript. Sequence comparison of the 700bp RT PCR product, p700-1 (SEQ ID NO. 24), with AtMYB103 shows 93% identity at the amino acid level, 99% identity in 5 the R2R3 region and 89% in the 3' region, although this sequence is incomplete (Figure 16). Further RT PCR was performed using primers designed from the gDNA sequence and first strand cDNA obtained from immature B. napus flowers as template. The first 10 round of PCR was performed using primers SRK1 and SRK7 situated at the 5' end upstream of the ATG start and at the 3' end including the TGA stop respectively. No products of the expected size were observed following electrophoresis on an agarose gel. A second round of PCR was performed using the first round PCR products as template with SRK2, a primer 180bp downstream of SRK1, and SRK7. This time a 15 product of approximately 800bp was amplified which corresponds to the expected size of 805bp (Figure 17). Cloning and subsequent sequencing of this product (p800-19 SEQ ID NO. 25)) shows 99% identity to the genomic BnMYBI03-1 sequence, with only three nucleotide differences. These differences may reflect the different cultivars used to produce the gDNA and cDNA libraries. Compared with AtMYB103 there is an 20 overall amino acid identity of 93%, with 99% identity in the R2R3 region and 89% identity in the putative activation domain (Figure 18). Screening of the B. napus flower cDNA library with a 350bp 3' probe (gene specific) derived from this RT PCR product failed to give any positive signals. 25 Using new primers designed from the AtMYB103 sequence another round of RT PCR was performed. First strand cDNA was generated from polyA+ RNA extracted from immature B. napus flower buds using the primer Z1346E10. This primer is situated at the 3' end of the gene and includes the TGA stop codon. This was used in a PCR with primers A5962H02, situated at the 5' end including the ATG start and Z1346E10. A 30 950bp product was generated, the approximate size predicted from the AtMYB103 sequence (Figure 19). This product was cloned (p900-10 - SEQ ID NO. 26)) and sequenced and shares 97% identity with AtMYB103 at the amino acid level (Figure 20). It also shares homology with p800-19 and BnMYBI03-1, although the greatest homology is with p7 0 0-1. 35 2638457_1 (GHMatters) P49763AU.1 11/04/11 58 A BLASTN and BLASTP search of the Genbank data base with p700-1, p800-19 and p900-10 all produce the most significant alignment with AtMYB103. Scores of 394 e 107, 428 e' 17 and 407 e" 11 respectively, were obtained at the nucleotide level. Scores of 520 e 14 1, 434 e1 2 ' and 450 e 126 respectively, were obtained at the amino acid level. 5 A Southern blot of B. napus genomic DNA probed with the 3' end of p700-1 (R. Kalla, personal communication) indicates that at least four different homologues of this gene are present in B. napus. Brassica napus which originates from a cross between B. rapa AA (n=1 0) and B. oleracea CC (n=9) contains an AACC genome. Southern blotting of genomic DNA from these parental species and probing with the same p700 10 1 probe provides evidence for at least two homologues in each organism (results not shown). The fact that these four clones, BnMYBI03-1, p700-1, p800-19 and p900-1 0, were isolated from B. napus flower buds and share significant identity with each other is in 15 keeping with the amphidiploid nature of B. napus. Their homology to AtMYB103 is in keeping with other Brassica genes that have been isolated in a similar manner. Figure 21 gives an overview of homology between these four clones and AtMYB103. It is likely that these four clones are homologues of AtMYB103. 20 BnMYBI03-1, a likely orthologue of AtMYB103 The Advanced BLAST2 and Orthologue Search Service at EMBL was used to find sequences likely to represent orthologues of BnMYB103-1. Using the BnMYB103-1 amino acid sequence as the query sequence the highest score of 1449 3.6e44 was obtained for AtMYB103. The other genes shown in this analysis are all MYB genes or 25 described as MYB-like. Further analysis using this service produced a species tree using the NCBI database and a gene tree based on the neighbour-joining tree computed by CLUSTALW (Figures 8 & 9). The taxonomic tree shows the closest evolutionary relationship between the B. napus 30 query sequence and the A. thaliana sequences. The sorting of genes according to this taxonomic tree groups BnMYBI03-1 with thirty-one A. thaliana sequences. Fifteen of these are MYB genes the others are described as MYB-related or transcription factor like proteins. 2638457_1 (GHMatters) P49763AU.1 11/04/11 59 Expression pattern of BnMYB103-1 The expression pattern of a gene may be determined using a variety of methods. Reporter genes such as gusA fused to a specific promoter are useful for determining temporal and spatial expression patterns. More sensitive and specific methods include 5 Northern blotting, RT PCR and in situ hybridisation. These techniques involve detection of mRNA that has been transcribed from the gene of interest. Where the gene under investigation is expressed only in certain tissues and at specific stages of development it is important to have reporter gene information regarding expression of the gene in the whole plant as guide to the selection of material. BnMYB103-1 10 promoter-gusA studies were followed by a more detailed analysis of BnMYBI03-1 expression using Northern blotting and RT PCR. BnMYBI03-1 promoter-gusA expression patterns A 725bp region upstream of the BnMYBI03-1 start site was cloned into the Sal l/Xba 1 15 sites of pBl1 01 .2 immediately upstream of gusA reporter gene. When transformed into A. thaliana, the X-Gluc stained inflorescences showed GUS staining only in the anthers of immature flowers. This corresponds to the staining pattern observed using the AtMYB103 promoter-gusA construct (Figure 22). Sections through these stained anthers show that GUS expression is found in the tapetum and microspores (Figure 20 23) Northern blot analysis of B. napus tissues The method used follows the protocol outlined by Ausubel et a. (1994) supra. Brassica napus tissues from different stages of development were selected for 25 analysis. These included the roots and shoots from ten day old seedlings, anthers harvested from flower buds 2-6mm in length, mature dehiscing anthers and flower buds of different sizes. The flower buds were divided into three groups representing different developmental stages, 0.5-2mm, 2.5-5mm and 6-8mm in length. Flower bud length has bec n correlated with the stages of anther and pollen development (data not 30 shown). Total RNA was extracted using Trizol reagent (Gibco). The integrity of RNA was assessed via Egarose gel electrophoresis. Absorbance readings on a spectrophotorr eter at 260 and 280nm were taken to assess the purity of RNA 35 extractions usi ig the A 2 6 0 to A 280 ratio. The A 2 6 G reading was also used to calculate the 26384571 (GHMatters) P49763.AU.1 11/04111 60 concentration of RNA in each sample. PolyA* RNA was extracted from total RNA using oligo dT dynabeads (Dynal) according to the manufacturer's instructions. For each sample, 750g of total RNA was used in the extraction to obtain approximately 3mg of PolyA* RNA. 5 A 474bp BnMYBI03-1 gene-specific probe was prepared from the 3' end of the sequence using PCR (96"C 3min x 1, 96*C 30sec, 50*C 30sec, 720C 30sec x 30, 72"C 5min x 1) using primers P16 and Z2346FO2 (Figure 24). To check for equal loading of polyA* RNA the filter was stripped and reprobed with a ubiquitin probe. The ubiquitin 10 probe, a 1.2kb fragment from the UBQ4 gene [Burke, (1988) Molecular and General Genetics 213: 435-443] was gel purified (Bresaclean kit, Geneworks) and labeled as described above. Figure 25 shows the results of probing with both the gene-specific and ubiquitin probes. The strongest signal with the gene specific probe is found in flower buds 0.5-2mm in length. A weaker signal is seen in pre-anthesis anthers. 15 Probing with ubiquitin indicates that the loading of polyA* RNA for each sample was even. Reverse transcriptase polymerase chain reaction for detection of BnMYB1 03-1 mRNA RT PCR is another sensitive and specific method for the detection of mRNA. The total 20 RNA samples used to prepare polyA' RNA for northern blotting were also used for RT PCR. The Onestep RT PCR kit (Gibco) was used to generate cDNA via reverse transcriptase and PCR was performed in the same tube. Tubulin primers were initially used to assess whether RT PCR products could be 25 obtained from the RNA samples (500C 30min x 1; 940C 2min x1; 94"C 30sec, 450C 30 sec, 72"C 60sec x 25; 72*C 1 0min x 1). The primers were designed using the published sequence of A. thaliana El-8 tubulin [Snustad, 1992 The Plant Cell4: 549 556]. A product of 545bp is expected from cDNA using the tubulin primers. A product from contaminating genomic DNA would be 760bp as the primers span two introns. All 30 of the samples tested with tubulin primers produced a strongly amplified product of the correct size (Figure 26). Two pairs of BnMYB103-1 specific primers were tested for their ability to produce a RT PCR product using RNA from pre- and post-anthesis anthers. The primer pairs employed were A5956A10 & A2485F04 and A5962H02 & Z1 346E1 0 with fragments of 784bp and 979bp expected from cDNA respectively. 35 RNA from pre-anthesis anthers gave a strongly amplified product of -784bp with 26384571 (GHMatters P49763AU.1 11/04/11 61 primers A5956A10 & A2485F04 while primers A5962H02 & Z1346E10 generated a product of -979bp. No product was seen when RNA from post-anthesis anthers was used as template (Figure 27). 5 The remaining RNA samples were then used as templates in RT PCR with primers A5962H02 & Z1346E10. Products corresponding to the size expected for BnMYB103 I were only obtained from RNA isolated from pre-anthesis anthers and flower buds 0.5-2mm in length (Figure 26). 10 These RT PCR results agree with the Northern blotting data and BnMYB103-1 promoter-gusA experiments. Expression of BnMYBI03-1 is restricted to pre-anthesis anthers and is most strongly expressed in flower buds 0.5-2mm in length. At this stage of development the pollen exists as meiocytes, tetrads and newly released, pre-mitotic microspores and the tapetum shows its highest secretory activity. 15 b) BnMYB103-2 The second orthologue of AtMYB103 is named BnMYBI03-2 and its nucleic acid sequence and putative amino acid sequence are provided in Figure 2. 20 Example 3 - Ortholoques of the MYB genes BLAST searching of the GenBank database has identified putative orthologues of BnMYB32, namely GhMYB9 from cotton (Figure 5b) TMH27 from tomato (Figure Sa) and AtMYB32 from wheat (Triticum aestivum) (Figure 36). 25 BLAST searching of the GenBank database has identified putative orthologues of BnMYBI03-1, namely OsMYBI03 from rice (Figure 6 and Figure 37). BLAST searching of the wheat Grain gene database (http:/wheat.pw.usda.qov) identified a putative orthologue of AtMYB103 from wheat (Triticum aestivum) (Figure 38). 30 The wheat and rice putative sequences were used to clone the orthologue genes. The wheat orthologue TaMYB32 was cloned using RT-PCR with nested primers. The deduced amino acid sequence exhibits 63 % identity to the AtMYB32 sequence 35 (Figure36). 2638457_1 (GKMatters) P49763.AU.1 11/04/11 62 A homologous fragment of AtMYBI03 from rice (Oryza sativa) anther cDNA was cloned using primers Tr-F1 and Tr-R2 (see Figure 37). The fragment includes part of the R3 sequence and sequence immediately downstream from R3. The rice orthologue 5 of AtMYB1 03, termed OsMYB1 3, exhibits a high level of sequence identity to AtMYB103 at the amino acid level. Figure 38 shows an alignment of the deduced amino acid sequences of AtMYB103 and a fragment of its wheat orthologue TaMYB1 03. Underlined amino acids are 10 identical. The deduced amino acid sequence is about 90% identical to that of AtMYB103 sequence (Figure38). Example 4 - Functional Analysis of the MYB genes Functional analysis of BnMYB103-1 15 A number of strategies are available to obtain information about the function of a specific gene. The expression of BnMYBI03-1 in immature anthers suggests a role in the development of the male reproductive structures. Homology with genes of known function may also provide some clue to function. BnMYBI03-1 is highly homologous to the A. thaliana gene AtMYB103. As previously stated, AtMYB103 is expressed in 20 the tapetum and developing microspores of A. thalana at the stage where meiocytes are dividing meiotically to produce microspore tetrads [Li, 1999 supra]. The spatial and temporal expression patterns of AtMYB103 imply a function in the regulation of pollen development. An estimated 20 000 mRNA transcripts are present in the mature pollen of Tradescantia paludosa and maize, reflecting the complex nature of pollen 25 development and presumably the requirement for regulatory genes. Mutants also provide important information about gene function. Transposon mutagenesis can be used to disrupt a specific gene and function implied from any consequent phenotypic changes. Moreover, the gene can then be cloned and function 30 verified using gene rescue. If the gene of interest is responsible for the mutant phenotype, the wild type phenotype will be regained. Mutagenesis has been used to generate a number of A. thaliana mutants that are defective in pollen development. 2638457_1 (GHMatters) P49763.AU.1 17/04/11 63 Antisense and sense techniques have been used in plants to disrupt the function of known genes. Many examples exist where a changed phenotype has been produced using this approach. Both techniques appear to silence expression of the endogenous gene being targeted. Post-transcriptional gene silencing (PTGS) has received 5 significant attention in recent years and some of the mechanisms involved are now beginning to be understood. The TA39 promoter Successful targeting of a specific endogenous gene using antisense and sense 10 constructs requires a strong tissue specific promoter. The promoter from a pollen/anther specific gene of tobacco, TA39, was selected for this work. This promoter is expressed in the microspores, connective tissue and most highly in the tapetum during early pollen development [Goldberg, 1993 supra]. 15 A TA39 promoter-gusA fusion (TA39::gusA) transformed into A thaliana or B. napus drove strong GUS expression in the young anthers (Figure 28). This expression pattern closely resembles that obtained with an AtMYB103 promoter fused to gusA [Li, 1999 supra]. AtMYB103 antisense and sense constructs driven by the AtMYB103 promoter had previously failed to produce a changed phenotype when transformed into 20 A. thaliana. Hence, the TA39 promoter was selected for use with the BnMYBI03-1 antisense and sense constructs. Antisense and sense BnMYB1 03-1 constructs The TA39 promoter was cloned as a 1.8kb BamHI/Sall fragment from p4AI-LIT into 25 pBluescript. An 800bp fragment of BnMYBI03-1, from the R3 repeat to the stop codon, was cloned as a BamHI fragment in front of the TA39 promoter. Restriction enzyme analysis (Pvull/SnaBI) identified constructs with the BnMYB103-1 fragment in both the sense and antisense orientation (Figure 29). The 2.6kb TA39::BnMYB103-1 Sacl/Sal fragment from each of these constructs was cloned into the binary vector 30 pB1101.2 for transfer into A. thaliana via root transformation (Figure 30). Characterisation of A thaliana transgenics transformed with antisense and sense BnMYB103-1 constructs It has been predicted that the expression of antisense constructs to Brassica anther 35 specific mRNAs in Arabidopsis may produce informative mutants...and even suggest a 2638457.1 (GHMatters) P49763AU.1 11104/11 64 function for the gene product. Transformation of A. thaliana and the generation of transformed plants for analysis can be accomplished in about two months. The same process in B. napus takes at least nine months. Taking these time frames into consideration, both A. thaliana and B. napus were transformed with the same 5 constructs. Considering the high degree of homology between AtMYB103 and BnMYBI03-1 it was felt likely that BnMYBI03-1 antisense and sense constructs would interfere with the expression of AtMYB103 in A. tha/iana plants. Following root transformation and selection for transformed tissue, individual plants 10 were grown for phenotypic analysis. The To plants were analysed for presence of the transgene using PCR with primers specific to the antisense or sense construct, respectively (Figure 31). Plants containing the transgene were then selected for further analysis. Pollen was taken from dehiscing flowers for analysis using the scanning electron microscope (SEM). 15 Table 1 summarizes the results of this analysis. The percentage of affected pollen ranges from <10% to 100% abnormal pollen. The abnormal pollen phenotype is variable with flattened, small, rounded or misshapen pollen resulting (Figures 32a & b). There appears to be no significant difference between the antisense and sense 20 constructs with regard to the percentages of abnormal pollen or the phenotypes observed. Table 1 - Scanning electron microscope analysis of transgenic A. tha/liana lines

T

0 plants PCR positive for T, plants PCR positive for Antisense construct sense construct LINE % ABNORMAL POLLEN LINE % ABNORMAL POLLEN ASI 90 S1 20 AS2 80 S2 20 AS3 90 S3 90 AS4 90 S4 80 AS5 90 S5 10 AS6 30 S6 80 AS7 90 S7 50 AS8 20 S8 50 2638457_1 (GHMatters) P49763AU.1 11/04/11 65 AS9 30 S9 40 AS10 100 S10 30 AS11 90 S11 90 AS12 <10 S12 40 AS13 10 S13 50 AS14 10 S14 10 AS15 90 S15 60 AS16 90 S16 10 AS17 10 S17 50 AS18 20 S18 30 AS19 100 S19 90 AS20 30 S20 100 AS21 40 S21 40 AS22 80 S22 90 AS23 30 AS24 90 AS25 60 AS26 100 AS27 50 AS28 70 AS29 90 All lines, no matter how severely the pollen phenotype was affected were able to produce viable seed. T, plants from selected lines were raised to determine whether the pollen phenotype observed in To plants would be carried over into the next 5 generation. Five of the most severely affected plants from each of the construct types were chosen. In each case the abnormal pollen phenotypes were maintained in the T 1 generation. PCR analysis of these plants confirmed the presence of the relevant transgene. 10 Characterisation of B. napus transgenics transformed with antisense and sense BnMYBI03-1 constructs Transformation of B. napus with the antisense and sense constructs was carried out and viability of transgenic pollen ascertained. All of the PCR positive transgenic plants contained viable pollen as determined by iodine staining. Scanning electron 2638457_1 (GHMatters) P49763AU.1 1110411 66 microscope analysis of pollen from these plants showed no significant abnormalities (results not shown). All of the transgenic lines produced viable seed. Crossing of antisense and sense lines 5 Waterhouse et al. (1998) PNAS 95:13959-13964 showed that transgenic tobacco transformed with both sense and antisense forms of the protease (Pro) gene from potato virus Y displayed greater levels of immunity to the virus than plants transformed with one or other of the constructs. 10 In an attempt to obtain a male sterile phenotype, antisense and sense lines from B. napus or A. thaliana and were crossed to obtain transgenic plants of each species carrying both transgenes. Plants shown to be PCR positive for either the sense or antisense transgene were selected for use as both male donors and female recipients. The pre-dehiscent anthers from newly opened flowers were removed and the stigma 15 inspected for the presence of pollen. A dehiscing anther from the male donor was then used to deposit pollen directly onto the stigmatic surface. Treated flowers were tagged with the relevant information and siliques allowed to develop. Seed from these siliques was germinated on selective media, GM kanamycin (50pg/ml) for A. thaliana, GM hygromycin (1 00pg/ml) for B. napus. Seedlings able to grow on these media were 20 transferred to soil and grown to maturity. The presence of both transgenes was confirmed with PCR using primers specific to each construct. Lines raised from each of these crosses were analysed for abnormal pollen phenotypes using the SEM. All of the A. thaliana lines showed abnormal pollen similar to that observed in the 25 antisense or sense parents. All of the plants produced viable seed, indicating that complete male sterility had not been achieved. The B. napus lines showed a range of phenotypes with up to 90% abnormal pollen, a feature not observed in either of the antisense or sense parents. Some of the plants generated from these crosses were PCR positive for only one of the transgenes, indicating a degree of self-fertilsation. As 30 these plants represent a T 1 population and may be homozygous for the transgene it was of interest to analyse their pollen. Some of these T 1 plants did show abnormal pollen phenotypes similar to those seen in A. thaliana. SEM analysis of these transgenic plants showed that the plants were able to produce viable seed. 2638457_1 (GHMatlers) P49763,AU.1 11/04/11 67 Pollen phenotypes Wild type A. thaliana and B. napus pollen both appear very similar, apart from an obvious size difference. An A thaliana WT pollen grain is approximately 30x1 5pm and a B. napus pollen grain approximately 40x20pm. Both are tricolpate with germinal 5 apertures that run the length of the grain and are positioned equidistantly. The exine has a characteristic network of ridges that form a regular pattern. Using the SEM a range of abnormal pollen phenotypes was observed in A tha/iana transformed with the sense, antisense or both constructs. Similar phenotypes are observed in T 1 sense and antisense B. napus plants or when both constructs are present. The abnormalities can 10 be divided into a number of categories: 1. Pollen exhibiting normal exine patterning but displaying abnormalities in shape, size and germinal aperture positioning; 2. Aborted pollen that appears small and deflated but with normal exine patterning; 3. Abnormally shaped grains that appear partially or fully deflated with normal exine patterning but coated in parts as if the contents have "oozed" out. In some cases, 15 pollen displaying this phenotype occurred in large clumps, apparently held together by the secreted contents; and 4. Pollen that is small and rounded. In many cases the abnormal pollen from BnMYBI03-1 sense and antisense transgenic A. thaliana and B. napus plants are larger than wild type. Abnormally large pollen from 20 A. thaliana showed an average increase of 15% in length and 30% in diameter. The largest increases observed were 26% in length and 46% in diameter. In B. napus the average increases were 5% in length and 13% in diameter. The largest increases observed were 10% in length and 30% in diameter. 25 Transmission electron microscope analysis of abnormal pollen Abnormal pollen grains from a number of A. thaliana lines transgenic for either the sense or antisense BnMYB103-1 transgene were selected for analysis using the transmission electron microscope (TEM). Thin sections through these pollen grains were compared with sections of wild type pollen at the same developmental stage. 30 The exine, intine, middle layer, tapetum and microspores of pollen from the transgenics all appear normal. No obvious differences can be detected in these sections. Example 5 - Production of Male Sterile Plants 35 From Example 4 it is shown, that at least in B. napus, blocking expression of BnMYB103 alone does not produce 100% sterile plants. The inventors propose that at 26384571 (GHMatters) P49763AU.1 11/04/11 68 least two and preferably three genes need to be blocked in B. napus to produce 100% male sterile plants. In an attempt to provide 100% male sterile plants in B. napus the following construct 5 containing a glucocorticoid (dexamethasone)-mediated transcriptional induction system was made. The strong TA39 promoter was incorporated in the system to ensure an adequate level of GVG is produced in developing anthers. Once activated by dexamethasone (DEX) GVG can induce the transcription from the chimeric promoter. A GUS reporter gene was placed under the control of the chimeric promoter to 10 examine the effectiveness of the system. Exact details of the construct are as follows, with reference to Figures 33 a & b and Figure 34: 15 The BamH1-digested BnMYBI03-1 fragment was blunt-ended and inserted into the EcoRV site of the plasmid containing BnMYBI03-2 sequence. The BamH1 AtMYB32 fragment was then ligated to the BamHl site of the resultant plasmid pBnMYB103-12 creating pMYB103-32 (all sequences in the same orientation) and pMYB103-23 (AtMYB32 in opposite orientation). The Xhol-Xbal fragments from the two plasmids 20 were cloned into the Xhol-Xbal sites of pLITMUS28 (New England Biolab) producing pLTMYB103-32 and pLTMYB103-23, respectively. The MYB fragments were then released from pLTMYB103-32 and pLTMYB103-23 using Spel restriction enzyme and inserted into the Spel site of pTADEX1 generating pTADEX31 and pTADEX32, pTADEX71 and pTADEX72, respectively. Plasmid pTADEX1 was constructed by 25 replacing the Sbfl-Pmel CaMV35S fragment in pTA7002 (Nam-Hai Chua, Rockefeller University USA) with a Pstl-EcoRV TA39 promoter fragment. The numbers marking the ends of the MYB fragments indicate the number of base pairs downstream from the translational start site (ATG). AtMYB32 sequence includes a translational start site at position 1 and a stop codon at position 822. Boxes represent promoters. 30 GVG encodes a chimeric transcription factor which binds to and activates the 6UAS promoter in the presence of dexamethazone. HPT gene encodes hygromycine phosphotransferase used for the selection of transgenic plants. 263457_1 (GKMatten) P49763AU.1 11/04111 69 The system was introduced into Arabidopsis plants and the GUS expression of four lines was examined. The GUS activity was detected only in the anthers sprayed with DEX (Figure 35B). Two allelic sequences of BnMYB103, BnMYB103-1 and BnMYB103-2 and one copy of AtMYB32 sequence were linked together in a sense or 5 antisense orientation. These fragments containing multiple MYB sequences were placed under the control of the chimeric promoter.The constructs were transformed into Arabidopsis plants and PCR analysis was used to ascertain the presence of the transgenes in the plants. 10 The seed setting of 25 transgenic lines was examined in repsonse to the DEX spray and eight of these lines exhibited abnormality in seed setting. The majority of the siliques (50-95%) in these lines failed to elongate (aborted (Figure 35H) and the elongated siliques contained fewer seeds than the untreated siliques. These transgenic lines produced abnormal pollen in response to DEX induction (Figure 35F). 15 Most of these abnormal pollen are devoid of contents as demonstrated by Alexander staining and the presence of aggregates inside the pollen sacs (Fig 35D). However, the gynoecia of the male sterile flowers remained fertile as cross-pollination with untreated pollen restored the seed setting. 20 Example 6 - A repressorlrestorer male sterility system Transcription repressors use various repressive motifs to block the transcription of their target genes. One of the plant repressive motifs consists of about twelve amino acids (LDLDLELRLGFA (SEQ ID NO: 27), or LDLNLELRISPP (SEQ ID NO: 28)). The two 25 peptide sequences exhibit nine identical or homologous residues. The repressive motif (LDLDLELRLGFA (SEQ ID NO: 27)) from Arabidopsis was fused to four different transcription factors with resultant loss-of-function phenotypes demonstrating that the motif converts transcription factors into strong dominant repressors. Inspection of AtMYB7 (Li, S.F., Parish, R.W. (1995) Plant J. 8, 963) and AtMYB32 C-terminal 30 sequences identified the repressive sequence (LDLNLELRISPP (SEQ ID NO: 28)). The strategy is to convert AtMYB1 03 into a strong repressor using the motif of twelve amino acids to obtain male sterility. The heterozygous male sterile inbred A containing the chimeric AtMYB1 03 repressor (AtMYB103Rep) is crossed with inbred B containing 35 a "restorer" to produce male fertile F1 hybrid seeds (Figure 44). The "restorer" will be AtMYB103 gene under the control of the strong anther-specific At39 promoter or 2638457_1 (GHMatters) P49763AU.1 11/04/11 70 multiple copy of the AtMYB103 promoter or their equivalents. Higher levels of the AtMYB1 03 protein (activator) in the hybrid plants will alleviate the repression by AtMYB103Rep protein leading to viable pollen production and seed setting. 5 The system produces 50% male fertile inbred A seedlings. A selectable marker linked to the repressor will provide a selection to cull the male fertile inbred A seedlings before crossing with inbred B. Alternatively, a simple chemical which can overcome the repression by the AtMYB103Rep may be used to induce seed setting of the male sterile plants to obtain the homozygous inbred A seed. The homozygous and male 10 sterile inbred A plants will then be crossed with inbred B plants to obtain F1 hybrid seed. The repressor/restorer reversible male sterility system is being successfully tested in Arabidopsis and is suitable for hybrid seed production in any crop plants including 15 canola and wheat. A sequence coding for the repressor motif of twelve amino acids, LDLDLELRLGFA (SEQ ID NO: 27), was fused in frame to the 3' end of the AtMYB103 coding sequence producing a chimeric fusion peptide. The chimeric gene was placed under the control 20 of the AtMYB103 promoter (Figure 39). The repressor construct was transformed into Arabidopsis plants and more than 50% of the sixty transformants exhibited male sterility. A restorer (activator) containing the AtMYB103 gene under the control of the At39 promoter was constructed (Figure 39). Eight Arabidopsis lines transgenic for the restorer were obtained and exhibited normal male fertility. Pollen from these restorer 25 plants was used to pollinate some male sterile plants containing the repressor construct and the F1 hybrid seeds were collected for further analysis. Example 7 - Further studies on the repressor/restorer male sterility system 30 In this experiment, an AtMYB103 insertion mutant is described, which exhibits complete male sterility with early tapetum degeneration and collapsed pollen. Loss-of function mutant plants were also obtained using an AtMYB103/EAR chimeric repressor. The plants are male sterile and the effects on tapetum and pollen development are similar to those observed in the insertion mutant. A restorer 35 containing the AtMYB103 gene driven by a strong anther specific promoter was able to 2638457_1 (GHMatters) P49763.AU.1 11/04/11 71 restore male fertility when introduced into the male sterile plants. The chimeric repressor and the restorer constitute a reversible male sterility system which can be adapted for hybrid seed production. This is the first reversible male sterility system targeting a transcription factor essential to pollen development. 5 Experimental procedures Plant materials and growth Arabidopsis thaliana accession Columbia (Col-0) was used for all gene transfer 10 experiments and wild-type controls. Plants were grown on soil under constant illumination or on germination media (GM) containing the appropriate selective antibiotic. The atmybl03 T-DNA insertion mutant line (line 320C12) was obtained from GABI-Kat (Max Planck Institute for Plant Breeding Research, Germany; http://www.gabi-kat.de). Seed was sown on GM containing 11.25 pg ml- 1 Sulfadiazine 15 to select for plants containing the T-DNA insert. Surviving plants were screened by PCR using the primers 103-52For and pAC161 Rev (Table 2) to confirm the T-DNA insertion in AtMYB103 gene. The primers 103-52For and 103+1474Rev which flank the T-DNA insert, were used in PCR reactions to determine the genotype of selection positive plants. 20 Plasmid construction The full-length AtMYB1 03 cDNA was amplified from Arabidopsis wild-type cDNA using the primers 103-3For and 103+1476Rev. The fragment was cloned into the pDrive vector (Qiagen) and sequenced. The fragment was excised from pDrive and inserted 25 into the Sma1 and Sac1 restrictions sites of the pBlAt39 vector. pBlAt39 contains a 1300 bp At39 promoter cloned into the Hindill and BamH1 sites of the pB 110 1

.

2 vector (Clontech). The resultant plasmid pP39/103 encodes an AtMYB1 03 protein fussed with the first 8 amino acids of At39. To construct plasmids pP103/103EAR and pP39/103EAR, a P103/103EAR fragment was amplified from Arabidopsis (Col) 30 genomic DNA using PCR with primers EAR103F and EAR103R. The EAR103R contains a sequence coding for the EAR motif fused in frame with the AtMYB103 sequence. The PCR fragment was cloned into plasmid pDrive and sequenced. The P39/103EAR fragment was amplified from the plasmid pP39/103 using PCR with primers At39-1260 and EAR1 03R. The PCR fragment was then cloned into the pDrive 35 and sequenced. The Sall-Hindill fragments of P103/103EAR and P39/103EAR were 2638457_1 (GHMatters) P49763.AU.1 11/04/11 72 then ligated to Sall-Hindlil sites of plasmid pCAMBIA1380 (CAMBIA, http://www.cambia.org), respectively. Plant transformations 5 Constructs were transformed into Agrobacterium tumefaciens strain GV3101. Arabidopsis thaliana (accession Col-0) was transformed by vacuum infiltration following the method described by Bechtold et al (1993) C.R. Acad. Sci. Paris, Life Sciences, 316, 1194-1199. To seed was sown on GM containing 50 pg miV kanamycin sulphate (pP39/103) or 15 pg ml 1 and hygromycin (pP103EAR, pP39/EAR) grown 10 under constant light at 22*C. Surviving transformants were verified by PCR amplification of the transgenes from genomic DNA using construct-specific primers. RT-PCR analysis Total RNA used in the RT-PCR experiments was isolated from young florets of soil 15 grown plants using Trizol Reagent (Invitrogen Inc., Figuresi and 8) or RNeasy plant kit (Qiagen, Figure 6). First strand cDNA synthesis was carried out according to the manufacturer instructions (Invitrogen: Superscripftm Ill reverse transcriptase and reagents). The conditions for PCR amplification of cDNA were as follows: first cycle, 94*C for 3min; second cycle, 94*C for 30sec, 550C for 30sec and 720C for 50sec; third 20 cycle, 720C for 10min. For the PCR reactions in Figure 6a and b, the annealing reaction was set at 480C for 30sec. Gene-specific primers were used for the amplifications of f-tubulin (TUB1, TUB2), AtMYB103 (103-137For and 103+1004Rev for Figure 1, 103-52For and 103+1004Rev for Figure 8, 103F5 and 103UTR for Figure 6 ), P39/103 (At39+4For, 103-1004Rev), P103/103EAR (103F5, EAR-RT). PCR 25 products were visualized by running on a 1.2% agarose gel stained with ethidium bromide and captured digitally using a UV video capture system. For non-reverse transcribed controls, the Superscript enzyme was omitted from first strand cDNA synthesis. 30 Floral sectioning Whole florets at varying stages of development were fixed in 6% glutaraldehyde and 4% paraformaldehyde in 50mM sodium phosphate buffer for 2h at 4*C following 2 15min of vacuum infiltration. Fixed tissue was dehydrated using the following ethanol series: 30, 60, 70, 90 and 100% followed by infiltration in LR white/ethanol. Florets 35 were embedded overnight at 65"C and sectioned using a Reichert ultramicrotome. 2638457_1 (GHMatters) P49763.AU.1 11/04/11 73 Sections (2.0pm) were stained with 0.25% safranin. Anther stages were classified according to Sanders et al. (1999) supra. Microscopy 5 The morphology of pollen grains from mature, soil-grown plants was examined using a JOEL JSM 6340F field emission scanning electron microscope (Tokyo, Japan). Mature pollen grains were examined at ambient temperature. Images were digitally captured at a working distance of 28mm at 2.0kV. Analysis of anther sections using transmission electron microscopy was carried out as described previously (Higginson et al., 2003 10 supra). Digital images were processed using ADOBE Photoshop version 5.5 and Microsoft Power Point and Office 2000. Results 15 Male sterility of an AtMYB103 insertion mutant An AtMYB103 insertion mutant line was obtained from the Max Planck Institute for Plant Breeding Research, Germany. The T-DNA insertion was identified in the 3' coding region of AtMYB103 gene approximately 54 bp upstream of the translational stop codon. The insertion creates a truncated protein with an 18 amino acid deletion 20 from its C-terminal (Figure 40A and B) and with the addition of an extra 36 amino acids encoded by the T-DNA sequence (Figure 40B). Sulfadiazine resistant plants were obtained with a 3:1 segregation ratio and homozygous plants identified using PCR analysis. The AtMYB1 03 mutant was found to be recessive. The insertion drastically reduced the level of truncated AtMYB103 transcript in the mutant, as shown by the 25 lower level of RT-PCR product from the mutant flowers (Figure 40C). The homozygous plants displayed complete male sterility and produced collapsed pollen grains with little cytoplasmic content (Figure 41 b and c). These pollen grains formed aggregates and could not be released from the anther locules. A few remaining pollen grains possessed abnormal pollen walls (Figure 41d and e). The siliques failed to elongate 30 (Figure 41a). The seed setting and silique elongation were restored using donor pollen from wild-type plants indicating that the gynoecium remained fertile in the insertion mutant. The male fertility of the insertion mutant was restored by a complementing construct containing the AtMYB103 gene (data not shown). The male sterile plants produced longer inflorescences, more flowers and exhibited an extended flowering 35 time. 26384571 (GHMatters) P49763.AU.1 11/04/11 74 The development of tapetum and pollen in the wild-type and mutant plants was examined in anther sections (Figure 42). Florets from the wild-type and mutants plants were fixed, embedded, sectioned and analysed. The tapetum and pollen in the mutant 5 appeared normal and indistinguishable from wild-type anthers up to stage 5 (Figure 42a and b). In wild-type anthers at stage 6, pollen mother cells entered meiosis and tapetal cells became vacuolated (Figure 42c; Sanders et al., 1999 supra). The mutant tapetum at stage 6 appeared slightly more vacuolated (Figure 42d) and this abnormality became more severe at stage 7 (Figure 42e and f), when pollen mother 10 cell meiosis had been completed and tetrads formed. In the wild-type anthers, the callose wall surrounding the tetrads dissolved at stage 8 releasing microspores (Figure 42g) and tapetum degeneration initiated at stage 10 (Senders et al., 1999 supra). However, some tetrads in the mutant failed to separate (Figure 42h) even though the callose surrounding the tetrads appeared to have been lost. The mutant tapetum 15 exhibited an advanced stage of degeneration at stage 9 (Figure 42i and j). At stage 12, most microspores in the mutant anther locules were collapsed and a few microspores containing cytoplasm were trapped among the debris (Figure 42k, I and m). The ultrastructure of the tapetum was further examined using transmission electron 20 microscopy. The mutant tapetum was more vacuolated than wild-type tapetum and pollen mother cells appeared normal at stage 6 (Figure 42n and o). The tapetum vacuolation became more pronounced at tetrad stage and tapetum degeneration clearly visible at about stage 9 (Figure 42p and q). By this stage, cellular debris was observed in the anther locules and no exine was deposited on the pollen wall (Figure 25 42q). These results indicate that disruption of the AtMYB103 gene leads to earlier tapetum degeneration and completely disrupts pollen development. The phenotype effects resemble those obtained using antisense technology (Higginson et al., 2003 supra) but are more severe. 30 Male sterility induced by a chimeric AtMYB 103 repressor In order to regulate male sterility by interfering with AtMYB103 function, the possibility of creating a dominant AtMYB103 repressor was explored. The twelve amino acid EAR sequence has been shown to act as a dominant repression motif when fused with 35 other transcription factors (Hiratsu et al., 2003 supra). A short nucleotide sequence 2638457_1 (GHMatters) P49783.AU.1 11/04111 75 coding for the EAR sequence was fused in frame to the 3' end of the AtMYB1 03 open reading frame, generating an AtMYB103EAR fusion. The last amino acid (valine) in the AtMYB103 peptide was replaced by a glycine at the fusion joint (Figure 43A). The fusion construct was placed under the control of either the AtMYB1 03 promoter 5 (pP1 03/103EAR) or a strong anther specific promoter At39 (At5g59845) (pP39/103EAR) (Figure 43A), respectively. The At39 promoter is strongly expressed in developing Arabidopsis anthers with highest expression in the tapetum (unpublished results). 10 Arabidopsis plant lines transgenic for the constructs (about 60 lines per construct) were examined for pollen formation and seed setting. Approximately sixty percent of the pPl03/103EAR lines exhibited complete male sterility and silique abortion (Figure 43B, a and b), but only five percent of the pP39/103EAR lines did so. The At39 promoter was much less efficient in inducing male sterility than the AtMYB1 03 promoter, 15 presumably because it is activated slightly later in anther development than the latter promoter. The male sterility phenotype was stable through two to three generations in nine lines tested and segregated with the transgene. The pollen grains from the male sterile lines exhibited a range of morphologies, from partially to completely collapsed. The great majority of pollen grains in some of the male sterile lines were completely 20 collapsed and devoid of cellular contents (Figure 43B, c and d). Flower buds from the pP1 03/103EAR plants were sectioned and the anther sections (Figure 44) were compared with wild-type (Figure 42a, e, i and k). In the early stages of anther development, both the tapetum and microspore mother cells appeared 25 normal (Figure 44a). The mutant tapetum at stage 7 (tetrad stage) became more vacuolated and appeared to initiate its degeneration (Figure 44b) much earlier than the wild-type tapetum. The sporocytes had undergone callose deposition and completed meiosis to form tetrads. At stage 9, the callose surrounding the tetrads appeared to dissolve but some of the microspores were attached to each other (Figure 44c) 30 indicating that some callose remained. Most of microspores eventually degenerated and their remnants formed aggregates adhered to anther locule walls (Figure 44d and e). A few microspores contained some cytoplasmic contents and were trapped among the remnants. Hence, addition of the EAR sequence to the AtMYB1 03 protein results in anther and pollen phenotype similar to that obtained with the insertion mutant. 35 26384571_1 (GlMatters) P49763.AU.1 11/0411 76 The transcript levels of the P103/103EAR transgene and the endogenous AtMYB1 03 gene were determined in the developing flowers of five male sterile lines using RT PCR analysis (Figure 45). The RT-PCR product levels of the endogenous AtMYB103 transcript in the transgenic lines are similar to those found in wild-type plants (Figure 5 45a, lanes 1-10). The transgene RT-PCR product levels are also similar between lines (Figure 45b, lanes 1-10) but are somewhat higher than the levels of AtMYB1 03 product (Figure 45a and b). The f-tubulin product levels were included to indicate similar amounts of total RNA in the RT-PCR reactions (Figure 45c, lanes 1-10). Hence, addition of the EAR motif was highly effective in converting the MYB transcription 10 factor to a dominant repressor. Furthermore, the weak MYB promoter drove sufficient levels of expression to repress the activity of endogenous AtMYB103. The repressor/restorer system for hybrid seed production The possibility of utilizing the P103/103EAR transgene in a repressor/restorer male 15 sterility system was then determined. A repressor/restorer system requires a male sterility-inducing repressor incorporated into female lines (pollen recipients) and a restorer in male lines (pollen donors) (Figure 46). In this case, the restorer would consist of the AtMYB1 03 gene under the control of a strong anther specific promoter such as the At39 promoter (pP39/103). We postulated that in the F1 plants derived 20 from the cross, the high levels of the AtMYB1 03 protein would prevent the AtMYB1 03EAR fusion protein from repressing pollen production and male fertility be restored. Several Arabidopsis lines transgenic for the restorer (P39/103) were obtained and all 25 exhibited normal growth and seed setting. Analysis of the anthers and pollen grains revealed no abnormality (data not shown). The transcript levels of the transgene and endogenous AtMYB103 gene were examined in the developing florets of four lines using RT-PCR analysis. The RT-PCR product levels of the transgene P39/103 were much higher than those of the endogenous AtMYB1 03 gene in all four lines (Figure 30 47c, d and a, b). The fi-tubulin product levels of the four RNA samples were similar (Figure 47g and h, lanes 1, 2, 3, 4). The primers for the restorer RT-PCR were also used to amplify any genomic restorer DNA present in the RNA samples and lower levels of the genomic products were detected (Figure 47e and f). 26384571 (GHMatters) P49763AU. 111/04/11 77 Pollen grains from four pP39/103 lines were used to fertilize seven male sterile pP103/103EAR ines, including the four lines shown in Figure 45. The F1 plants were isolated in double selection media for both the repressor and restorer constructs. The F1 plants from thirteen crosses were examined for silique elongation. The silique 5 elongation was completely restored in one F1 line. Normal elongation of about seventy percent of siliques was observed in two F1 lines and about thirty percent in one line. The phenotype of silique elongation in F1 plants segregated with the restorer construct. The variability in restoration of male fertility probably relates to the stages of anther development when the At39 promoter is active (see Discussion). 10 Discussion AtMYB103 controls tapetum and microspore development. 15 As previously reported (Higginson et al., 2003 supra), down-regulation of AtMYB103 expression in flowers led to earlier tapetum degeneration and the formation of distorted pollen with reduced or no cytoplasmic content. However, these plants were able to set seed so viable pollen was produced for self-fertilisation to occur. In this experiment, a complete loss-of-function phenotype for AtMYB1 03 was obtained with both an 20 AtMYB103 insertion mutant and mutant plants transgenic for an AtMYB103/EAR chimeric repressor. The mutant plants generated using the two different approaches exhibited complete male sterility and similar developmental abnormalities of tapetum and pollen. The tapetum became highly vacuolated and degenerated prematurely. Microspores in many tetrads failed to separate at later stages and exine was not 25 deposited in the pollen wall. Almost all microspores collapsed and degenerated. These results indicate that premature tapetum degeneration reduces the enzymes responsible for callose degradation and prevents exine formation by limiting either the production or deposition of exine components. The absence of exine and the limited availability of other essential molecules for pollen development lead to pollen 30 degeneration. The results indicate the AtMYB103 gene is required for the maintenance of the tapetum during early microspore development, prior to the initiation of tapetum degeneration at stage 10. The AtMYB1 03 protein is most probably a transcription activator (see below) and may activate specific pathway(s) holding the tapetum degeneration process in check during the early stages of pollen development. 35 Disruption of the pathway(s) allows programmed cell death to proceed. 2638457_1 (GHMatters) P49763AU.1 11/04/11 78 AtMYB103 transcript was detected in trichomes using in situ hybridization and down regulation of AtMYB103 expression resulted in overbranched trichomes containing more nuclear DNA in Arabidopsis (Landsberg erecta) (Higginson et al., 2003 supra). 5 However, no visible change of trichome morphology was detected in the insertion mutant (Columbia). This variation may be related to the differences between the two Arabidopsis ecotypes. It was proposed that the AtMYB1 03 gene might control similar processes in trichomes 10 and tapetal cells, such as endoreduplication (DNA replication without cell division) in trichomes and polypioidization (cell divisions without cytokinesis) in tapetal cells (Higginson et al., 2003 supra). Hence the anther transcript levels of some of the genes required for cell cycle regulation were compared in anthers of wild-type plants and the insertion mutant. These genes code for a cyclin (CYCD3), cyclin-dependent kinases 15 (CDKA, CDKB1 and CDKB2), CDK inhibitors (KRP1 and KRP2) and histone H4. RNA samples were extracted from the wild-type and mutant anthers of stages 5 to 9, respectively, before the initiation of microspore mitosis at stage 11 and RT-PCR analysis carried out with gene specific primers. The RT-PCR product levels of these genes in the mutant anthers were similar to those in the wild-type anthers (data not 20 shown) indicating that the expression of these genes is not directly controlled by the AtMYB103 gene. While comparative microarray analysis using the wild-type and atmyb103 mutant anthers may identify large numbers of genes which are down regulated, as is the case in the rice udtl mutant, most of these genes are not the direct targets of the transcription factor and their down-regulation a consequence of the 25 premature disappearance of tapetal tissue. An inducible complementary system would be more appropriate for the identification of target genes. Mutations in several genes coding for transcription factors have been found to cause premature tapetum degeneration and pollen abortion. These genes include the rice 30 UNDEVELOPED TAPETUM 1 (UDT1) coding for a basic helix-loop-helix protein, Arabidopsis MALE STERILITY 1 (MS1) coding for a PHD-finger transcription factor and ABORTED MICROSPORES (AMS) encoding for a basic helix-loop-helix protein. The UDT1 protein shares 32% identity with the AMS protein. Silencing of the petunia TAPETUM DEVELOPMENT ZINC FINGER PROTEIN 1 (TAZI) gene also leads to 35 early degeneration of tapetum and pollen abortion. The tapetum in a atmyb33 and 2638457_1 (GHMatters) P49763AU.1 11/04/11 79 atmyb65 double mutant undergoes hypertrophy at the pollen mother cell stage resulting in partial male sterility. However, the fertility was restored under higher light intensity or at a lower growth temperature indicating that the two genes are not essential for tapetum development. 5 The chimeric repressor Several chimeric repressors driven by the CaMV35S promoter have been successfully used to induce loss-of-function phenotypes. This experiment represents the first example of a chimeric repressor under the control of its native promoter that induces a 10 loss-of-function phenotype. The P103/103EAR transgene was highly efficient in inducing male sterility, indicating that the levels of chimeric repressor transcript required for effective repression are relatively low and comparable to levels of the endogenous AtMYB103 transcript (Figure 45). As the AtMYB1 03 promoter is active only in early tapetum development, it may well be used to express other chimeric 15 repressors to obtain male sterility. The AtMYB1 03 protein was converted into a dominant negative repressor, implying it normally functions as a transcription activator or it interacts with an activator. Transcription activation domains are classified into three groups, namely acidic, 20 proline-rich and glutamine-rich. Inspection of the sequence outside of the MYB domain identified an acidic sequence of twenty-six amino acids at the C-terminus (256-282aa) with ten negatively charged and four positively charged amino acids. This putative activating domain may be repressed by the EAR motif in the chimeric repressor. However, it is unclear how the EAR motif exerts its repression effect. The repression 25 efficiency of the EAR motif was recently further demonstrated. Four genes coding for Arabidopsis transcription factors, namely APETALA3, AGAMOUS, LEAFY and AtMYB26, were fused with the EAR sequence and each driven by the CaMV35S promoter. Transgenic plants expressing the chimeric repressor exhibited a phenotype similar to the loss-of-function phenotype of the corresponding gene. 30 The restorer and reversible male sterility systems To construct a reversible male sterility system using the pP1 03/103EAR chimeric repressor, an effective restorer is required to restore male fertility to the F1 plants. The AtMYB1 03 gene under the control of a suitable anther specific promoter can act as a 35 restorer. A proof of concept for the system was obtained using the strong anther 26S38457_1 (GHMatters) P49763.AU.1 11/04/11 80 specific promoter At39 to drive expression of the AtMYB1 03 gene. The pP391103 construct was able to restore male fertility in some lines. Multiple copies of the AtMYB103 gene driven by its own promoter (AtMYB103 genomic clone) may prove to be a more effective restorer. Alternatively, a modified and stronger AtMYB1 03 5 promoter may also be used for expression. We have identified a short sequence immediately upstream from the TATA box of the AtMYB1 03 gene that is essential for tapetum expression and multiple copies may provide a means of increasing expression. Similarly in the barnase/barstar system driven by a tapetum-specific promoter TA29, identification of efficient restorer (barstar) lines in Brassica juncea 10 (Indian oilseed mustard) proved to be difficult. Only one in 54 cross-combinations between male sterile and restorer lines adequately restored F1 male fertility. The inability to identify more cross-combinations restoring male fertility was attributed to insufficient levels of barstar protein (inhibitor to barnase) at the appropriate developmental stages. An efficient restorer was obtained by incorporating into a 15 transforming construct two barstar transcription units driven by the TA29 and A9 promoters, respectively. The work in this experiment provides the first example of a transcription factor targeted to achieve reversible male sterility. The system can be adapted to crop plants for 20 hybrid seed production. AtMYB103 homologs occur in crop plants such as canola, rice and wheat. These homologs are also expressed in anthers (our unpublished results). Transgenic male sterility has been generated using a number of transgenes. The male sterility induced by the transgenes has provided valuable information regarding anther 25 and pollen development. However, their potential commercial application for hybrid seed production is limited by the lack of efficient and economical methods to maintain (multiply) the male sterile lines and/or the lack of suitable restorers. The barnase/barstar system has been used successfully for the commercial production of hybrids. The system contains an efficient restorer but suffers from an inability to obtain 30 plants homozygous for the sterility-inducing transgenes as the hemizygous plants are male sterile. A male sterile line is maintained by crossing with an isogenic wild-type line. Consequently, half of the progeny are male fertile. One strategy for removing the male fertile progeny has been to link a herbicide-resistant gene to the transgene and spray the progeny plants with the herbicide in a hybrid seed production field. Extra care 35 is required to eliminate all fertile plants to ensure the purity of the hybrid seed. The 2638457_1 (GHMatters) P49763AU.1 11/04/11 81 elimination of fertile progeny requires twice as much female parent seed, which could limit the applicability of the system in crops with a low multiplication factor (low number of seeds per plant) such as wheat. Furthermore, the spraying results in uneven distribution of female plants and reduces hybrid seed yield in some crops such as corn. 5 An inducible component (activator) can be incorporated into the AtMYB1 03 system to produce homozygous female lines. The activator is identical to the restorer except that it contains a ligand-binding domain of the ecdysone receptor (EcR) fused in frame with AtMYB103 (103EcR) (Figure 49A). The ecdysone receptor is advantageous over other receptors as it is the target of several commercially available insecticides (ecdysone 10 agonists). These non-steroidal ecdysone agonists have been used in many field applications. The 103EcR may be linked to the chimeric repressor 103EAR. The 103EcR chimeric protein remains inactive in the absence of ecdysone agonist but is activated to restore male fertility following agonist spraying. Hence, a male sterile and homozygous female line can be generated and maintained with agonist spraying 15 (Figure 49A). In a hybrid seed production field, all female plants are male sterile and no spraying is required. Hence the reversible male sterility overcomes the disadvantages associated with the herbicide strategy. Furthermore, it requires agonist spraying over a smaller acreage only for the multiplication of female lines. We have successfully tested a similar inducible component in the insertion mutant. 20 The chimeric repressor can also be modified to generate an inducible male sterility system which does not require a repressor (Figure 49B). The ligand-binding domain of the ecdysone receptor is fused with the chimeric repressor and introduced into a female line. Upon spraying with an ecdysone agonist, the chimeric repressor is 25 activated to induce male sterility. The homozygous female line is male fertile and becomes male sterile when sprayed with an ecdysone agonist in a hybrid seed production field (Figure 49B). 30 Table 2 Primer sequences 35 2638457_1 (GHMatters) P49763.AU.1 11/04/11 82 *The first nucleotides of the coding sequences are designated +1. Name Gene Position* Nucleotide sequence (SEQ ID NO:) EAR-RT EAR AGTTCAAGGTCCAAATCTAAA (51) EAR103R 103 +1471 ATGGAAGCTTACGCAAATCCTAGCCTGAGTTCAAGGTC (52) EAR CAAATCTAAACCCATATGATTGATGAGATCATCAG (53) EAR103F 103 -1105 AAGGTCTAGAGGCAAGGAGCTTCTATGGCCAA (54) 103UTR 103 +1506 GAAAAAGGAAAAAACTTAGAACCA (55) 103F5 103 +326 TATCATTGTCAAGTTTCACTCTGTT (56) 103-137For 103 -137 TCTTTGGGTGGGGCAATCTTTGAT (57) 103-52For 103 -52 AAGAGTAATCAAATCGATCAAGAGA (58) 103-3 103 -3 5'AGCCCCGGGCAAATGGGTCGGATTCCATGTTGT3'(59) 103+1004Rev 103 +1004 GAGCAAGTGAAGCATCTCGTCCTTG (60) 103+1474Rev 103 +1474 CGACAGCTGTCAAACCATATGATTGATGAGATC (61) 103+1476Rev 103 +1476 5'GCTGAGCTCAATCAAACCATATGATTGATGAG3'(62) At39+4For 39 +4 TATTTCCCGGCTGTAAAAGTTCTTCTTATTA (63) At39-1260 39 -1264 AAGGTCTAGAGTTCCCATGCCTTTAGATTCGGA (64) pAC161Rev TDNA LB GGGCTACACTGAATTGGTAGCTC (65) TUB1 Tubulin +309 GGACACTACACTGAAGGTGCTGAG (66) TUB2 Tubulin +1065 GGCTCTGTATTGCTGTGATCCACG (67) 26384571 (GHMatters) P49763.AU,1 1104/11

Claims (17)

1. A nucleic acid construct comprising: (a) a nucleic acid molecule encoding AtMYB103 (SEQ ID NO: 22) or encoding an orthologue of AtMYB103 having at least 75% sequence identity to SEQ ID NO: 22, or encoding a variant of AtMYB1 03 comprising a fragment of at least 150 amino acid residues having at least 85% sequence identity to SEQ ID NO: 22, and (b) a repressor motif.

2. The construct of claim 1, in which the orthologue has the sequence provided in SEQ ID NO: 3, SEQ ID NO: 5 or SEQ ID NO: 20.

3. The construct of claim 1, in which the variant comprises SEQ ID NO: 18 or up to amino acid residue 168 of SEQ ID No: 18.

4. The construct of any one of claims 1 to 3, in which the repressor motif is an EAR repressor motif encoding amino acid sequence LXLXLX (SEQ ID NO: 29) where L is Leucine and X represents any amino acid residue.

5. The construct of claim 4, in which the repressor motif encodes LDLNLELRISPP (SEQ ID NO: 28) or LDLDLELRLGFA (SEQ ID NO: 27).

6. A reversible male sterility system comprising: (a) a nucleic acid construct comprising a repressor motif fused in frame to the 3' end of a nucleic acid molecule encoding AtMYB1 03 (SEQ ID NO: 22) or encoding an orthologue of AtMYB103 having at least 75% sequence identity to SEQ ID NO: 22, or encoding a variant of AtMYB1 03 comprising a fragment of at least 150 amino acid residues having at least 85% sequence identity to SEQ ID NO: 22, and (b) a restorer construct comprising a chimeric molecule encoding AtMYB103 (SEQ ID NO: 22) or encoding an orthologue of AtMYB103 having at least 75% sequence identity to SEQ ID NO: 22, or encoding a variant of AtMYB103 comprising a fragment of at least 150 amino acid residues having at least 85% sequence identity to SEQ ID NO: 22, under the control of a strong anther specific promoter or multiple copies of an MYB1 03 promoter. 2681660_1 (GHMatters) P49763.AU 1 24/05/11 84

7. The system of claim 6, in which the repressor motif utilised is that according to any one of claims 1 to 5.

8. The system of claim 6, in which the strong anther specific promoter comprises an At39 promoter or a TA39 promoter.

9. Use of the construct of any one of claims 1 to 5 for producing a male sterile plant.

10. A plant cell transformed with the construct of any one of claims 1 to 5.

11. A transgenic plant comprising a plant cell transformed with the construct of any one of claims 1 to 5.

12. Progeny of the transgenic plant of claim 11.

13. Seeds, tissues, roots, shoots, tubers or propagating material of the transgenic plant of claim 11 or the progeny of claim 12 comprising the construct of any one of claims 1 to 5.

14. The plant cell of claim 10, plant of claim 11 or progeny of claim 12, in which the plant is monocotyledonous or dicotyledonous.

15. The, plant cell of claim 10, plant of claim 11 or progeny of claim 12, in which the plant is a legume, crop, cereal, native grass, fruiting plant or flowering plant.

16. The plant cell of claim 10, plant of claim 11 or progeny of claim 12, in which the plant is a Brassicaceae or other Solanaceae species, including potato and cole vegetables, cabbage, kale, collards, turnips, rutabaga, kohlrabi, Brussels sprouts, broccoli and cauliflower, mustards and oilseeds, crucifers, canola, tomato, grain legumes, wheat, barley, maize, tobacco and rice.

17. The construct of claim 1, the system of claim 6, the plant cell of claim 10, the plant of claim 11, the progeny of claim 12, or the use of claim 9, substantially as hereinbefore described, with reference to the examples, and, or figures. 2681660_1 (GHMatters) P49763.AU.1 24/05/11