Typescript (photocopy). / Digitized by Kansas Correctional Industries

Digitized by Kansas State University Libraries

Digitized by Kansas Correctional Industries

xi, 252 leaves : ill., tables, photos ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1977) from the Dept. of Agronomy, University of Adelaide

Meiosis is a cell division process central to the life cycle of all sexual eukaryotic organisms. Chromosome pairing, genetic recombination and subsequent nuclear division during meiosis produces four genetically distinct haploid gametes from a single diploid cell. Allohexaploid wheat ( Triticum aestivum ) behaves meiotically as a diploid, despite the existence in the genome of three closely related ( homoeologous ) genomes, A, B and D. Chromosome pairing during prophase I of meiosis in wheat is restricted to true homologous chromosomes, the result being the formation of 21 bivalents at meiotic metaphase I. The genetic control of chromosome pairing in wheat is under the control of several pairing homoeologous ( Ph ) genes, located predominantly on chromosome groups 3 and 5. The major suppressors of homoeologous pairing are Ph1 and Ph2. Their cytogenetic effect has been intensively studied but at the molecular level little is known about their function. The isolation and characterisation of Ph genes from wheat would lead to greater understanding of chromosome pairing mechanisms in complex allopolyploids, and may enable development of effective strategies for alien gene introgression from related species to modern wheat cultivars. In this study, several genomics - based approaches were adopted to explore the expressed portion of the wheat genome in order to identify and characterise genes that could function in the molecular processes regulating meiosis. The first approach used comparative genetics to characterise the region deleted in the ph2a mutant ( a deletion mutant at Ph2 ). The rice genomic region syntenous to that deleted in the ph2a mutant was identified through comparative mapping and used in searches of wheat databases to identify ESTs with significant similarity. Southern analysis confirmed a syntenous relationship in the wheat and rice genomic regions and defined precisely the position of the breakpoint in ph2a. What seems to be a terminal deletion on 3DS is estimated to be approximately 80 Mb in length. We can tentatively predict the identification of approximately 220 genes from the region deleted in ph2a. The putative role of identified candidate Ph2 genes is discussed. The second approach explored the validity of recent proposals suggesting the presence of a meiotic gene cluster in the region of Ph2. The transcriptional characteristics of genes linked to Ph2 were investigated using data from wheat EST databases in combination with recently developed analysis software. The tissue - distribution of mRNAs derived from genes linked to Ph2 is shown to resemble that of other large chromosomal regions in the wheat genome. It is concluded that the apparently high number of genes from the Ph2 region expressed in wheat meiotic tissue is not indicative of a meiotic gene cluster in this region, but rather highlights the transcriptional complexity of meiotic anther tissue. Finally, the meiotic expression pattern of approximately 1800 wheat genes was examined using cDNA microarrays. Two approaches were taken. Firstly, the applicability of microarrays to identify differentially expressed genes between wild - type anthers and anthers of three Ph mutant genotypes was investigated. These experiments failed to reveal significant down - regulation of genes in Ph mutant anthers compared to wild - type. Possible explanations are discussed. Secondly, the expression of all microarray clones was examined from pre - meiotic interphase through to the tetrad stage of meiosis. A number of candidate wheat genes involved in meiotic and anther developmental processes have been identified and are discussed. Prior to this study, the methods available to identify wheat meiotic genes, in particular as candidates for Ph2, were limited. The recent development of genomics in plant biology provided an opportunity for a new approach towards gene discovery and genome structural analysis in relation to meiosis. This research illustrates the need for, and the effectiveness of a new approach to study meiosis, contributing to our knowledge of the structural and functional characteristics of genes linked to Ph2, and establishing a strong basis for further wheat meiotic gene characterisation. / Thesis (Ph.D.)--School of Agriculture and Wine, 2003.

Spike morphology characteristics and the free-threshing habit of wheat have been extensively investigated because of their evolutionary significance and practical importance. Several genetic systems that govern these traits have been reported. Some studies suggest polygenic inheritance while others have identified major genes. This study was conducted to identify and locate quantitative trait loci (QTL) affecting the free-threshing habit and spike morphology characteristics in the International Triticeae Mapping Initiative (ITMI) recombinant inbred line (RIL) mapping population. The ITMI population was planted in three environments in 1999 and 2000. The ITMI RILs were evaluated for threshability and spike morphology characters. QTL analyses were performed using simple and composite interval mapping procedures. Two QTLs, one on chromosome lB and one on 4A, affecting spike length were identified. The QTL on chromosome 1B has not been described previously. One QTL controlling spikelet number was also detected on chromosome 4A. This QTL coincided in location with the QTL on chromosome 4A that affected spike length. One QTL controlling rachis internode length, a measure of spike compactness, was detected on chromosome 6A. The location of QTLs that affected spike length, spikelet number, and spike compactness did not coincide with the location of major genes (Q, C, S1, Ppd1, and Ppd2) known to affect these traits. Two QTLs, one on chromosome 2D and one on 4D, affecting threshability were identified. The QTL on chromosome 4D has not been described previously. A QTL that affected glume tenacity was also detected on chromosome 2D. Coincident QTLs on chromosome 2D that affected both threshability and glume tenacity are believed to correspond to Tg, a gene for tenacious glumes. In addition, an amplified fragment length polymorphism (AFLP) marker (XorstP3747207) that was putatively associated with Tg was identified using bulked segregant analysis. A QTL on chromosome 5A affecting glume tenacity was also identified. The QTL on chromosome 5A is believed to represent Q, a gene known to affect rachis fragility and glume tenacity. Information on the number, position, and effect of QTLs determining these traits and their associated molecular markers may facilitate their manipulation for wheat improvement purposes. / Graduation date: 2002

Graduation date: 1996

Thesis--Paris. / Bibliography: p. [303]-307.

Thesis--Toulouse. / Bibliography: p. [455]-467.

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