No description available.

Title page, contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / Cotton fibres are single-celled hairs, arising from the epidermal surface of the cotton ovule. One factor in determining the length of the mature cotton fibre is the timing of fibre initiation, which is therefore a crucial step in obtaining commercial cotton fibres. To achieve a greater understanding of the regulation of cotton fibre differentiation, more fundamental information is needed on the signals and mechanisms associated with fibre initiation. The extensive genetic knowledge of Arabidopsis leaf trichomes could aid in the elucidation of the genetic mechanisms controlling cotton fibre differentiation. Trichomes are small hairs on the plant surface, originating from single epidermal cells in a developmental process that appears very similar to that of cotton fibres. Arabidopsis trichome development has been extensively investigated, and several genes that control the process have been characterised. One gene essential for trichome initiation is TRANSPARENT TESTA GLABRAI (TTGI), and loss-of-function mutations in TTGI result in an almost complete absence of leaf trichomes. TTG 1 plays additional roles in numerous pathways in Arabidopsis, including root hair initiation, anthocyanin production and seed coat mucilage production. In order to isolate genes required for fibre initiation in cotton, functional homologues of Arabidopsis TTG 1 in cotton have been sought. Four putative homologues of Arabidopsis TTG 1 have previously been isolated in this laboratory by RT-PCR of mRNA prepared from cotton fibres, and are termed GhTTG 1-4. Sequence comparisons between the four cotton deduced proteins and Arabidopsis TTG 1 showed that they form two groups, with GhTTG 1 and GhTTG3 being closely related to each other (87% identical and 93% similar) and to TTG 1 (79% and 80% amino acid identity respectively). GhTTG2 and GhTTG4 formed the second group, with 95% amino acid identity to each other and lower (approximately 62%) identity to TTG 1. An analysis of the genomic origins of the GhTTG genes demonstrated that each is derived from the same ancestral diploid genome. Cross-species complementation experiments were performed to test for functional homology of these cotton TTG I-like genes to AtTTG 1, by introducing the cotton genes into Arabidopis ttgI-I mutants via Agrobacterium-mediated transformation. This experiment showed that two of the four genes, GhTTGl and GhTTG3 were able to restore trichome initiation in the Arabidopsis mutant plants, and a further investigation of GhTTG3 transgenic plants demonstrated complementation of the full range of ttgl mutant phenotypes. An analysis of the temporal and spatial expression of the GhTTG genes in cotton is also described. It was shown that each of the genes is expressed ubiquitously throughout the cotton plant, in common with many plant WD-repeat genes. A closer examination of transcript abundance in the developing cotton ovule utilising in situ hybridisation revealed predominant expression of GhTTG lIGhTTG3 in the epidermal cells destined to become cotton fibres. A yeast two-hybrid assay was utilised to identify transcription factors that may interact with GhTTG3 during .fibre development. This experiment identified three cotton fibre cDNAs encoding putative interacting proteins, including one with a similar secondary structure to several TTG I-interacting proteins in Arabidopsis, raising the possibility of similar regulat01;y-complexes controlling trichome initiation in Arabidopsis and cotton. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1262004 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2007

Title page, contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / Cotton fibres are single-celled hairs, arising from the epidermal surface of the cotton ovule. One factor in determining the length of the mature cotton fibre is the timing of fibre initiation, which is therefore a crucial step in obtaining commercial cotton fibres. To achieve a greater understanding of the regulation of cotton fibre differentiation, more fundamental information is needed on the signals and mechanisms associated with fibre initiation. The extensive genetic knowledge of Arabidopsis leaf trichomes could aid in the elucidation of the genetic mechanisms controlling cotton fibre differentiation. Trichomes are small hairs on the plant surface, originating from single epidermal cells in a developmental process that appears very similar to that of cotton fibres. Arabidopsis trichome development has been extensively investigated, and several genes that control the process have been characterised. One gene essential for trichome initiation is TRANSPARENT TESTA GLABRAI (TTGI), and loss-of-function mutations in TTGI result in an almost complete absence of leaf trichomes. TTG 1 plays additional roles in numerous pathways in Arabidopsis, including root hair initiation, anthocyanin production and seed coat mucilage production. In order to isolate genes required for fibre initiation in cotton, functional homologues of Arabidopsis TTG 1 in cotton have been sought. Four putative homologues of Arabidopsis TTG 1 have previously been isolated in this laboratory by RT-PCR of mRNA prepared from cotton fibres, and are termed GhTTG 1-4. Sequence comparisons between the four cotton deduced proteins and Arabidopsis TTG 1 showed that they form two groups, with GhTTG 1 and GhTTG3 being closely related to each other (87% identical and 93% similar) and to TTG 1 (79% and 80% amino acid identity respectively). GhTTG2 and GhTTG4 formed the second group, with 95% amino acid identity to each other and lower (approximately 62%) identity to TTG 1. An analysis of the genomic origins of the GhTTG genes demonstrated that each is derived from the same ancestral diploid genome. Cross-species complementation experiments were performed to test for functional homology of these cotton TTG I-like genes to AtTTG 1, by introducing the cotton genes into Arabidopis ttgI-I mutants via Agrobacterium-mediated transformation. This experiment showed that two of the four genes, GhTTGl and GhTTG3 were able to restore trichome initiation in the Arabidopsis mutant plants, and a further investigation of GhTTG3 transgenic plants demonstrated complementation of the full range of ttgl mutant phenotypes. An analysis of the temporal and spatial expression of the GhTTG genes in cotton is also described. It was shown that each of the genes is expressed ubiquitously throughout the cotton plant, in common with many plant WD-repeat genes. A closer examination of transcript abundance in the developing cotton ovule utilising in situ hybridisation revealed predominant expression of GhTTG lIGhTTG3 in the epidermal cells destined to become cotton fibres. A yeast two-hybrid assay was utilised to identify transcription factors that may interact with GhTTG3 during .fibre development. This experiment identified three cotton fibre cDNAs encoding putative interacting proteins, including one with a similar secondary structure to several TTG I-interacting proteins in Arabidopsis, raising the possibility of similar regulat01;y-complexes controlling trichome initiation in Arabidopsis and cotton. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1262004 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2007

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 161-172). Available also in a digital version from Dissertation Abstracts.

A network of three classes of proteins consisting of bHLH and MYB transcription factors and a WD40 repeat protein - TRANSPARENT TESTA GLABRA1 (TTG1) act in concert to activate trichome initiation and patterning in Arabidopsis. These proteins also regulate the flavonoid-based pigment biosynthetic pathway in almost all higher plants including Arabidopsis. Using TTG1-YFP translational fusions, I show that TTG1 is expressed ubiquitously in Arabidopsis leaves and is preferentially localized in the nuclei of trichomes at all developmental stages. Using conditional transgenic alleles I demonstrate that TTG1 directly regulates the same genes as GL3. In vivo binding of GL3, GL1 and TTG1 to the promoters of GL2, TTG2, CPC and ETC1 establishes that these genes are major transcriptional targets for the TTG1-bHLH-MYB regulatory complex. By co-precipitation, I confirm that TTG1 interacts with the GL3 (bHLH) and GL1 (Myb) proteins in vivo, forming a complex. The loss of members of the TTG1 complex through mutation, affects the subcellular distribution of other complex members. Using particle bombardment, I show that TTG1, GL3, GL1 and GL2 do not move between adjacent epidermal cells while CPC does move to neighboring cells. These data support a model for the TTG1 complex directly regulating activators and repressors and the movement of repressors to affect trichome patterning on the Arabidopsis leaf. In addition, I also show that GL3 is recruited to its own promoter in a GL1-independent manner, which results in decreased GL3 expression, suggesting the presence of a GL3 negative auto-regulatory loop. Expression studies using GL3-GR (GL3-glucocorticoid receptor) and TTG1-GR fusions reveal direct regulation of the late anthocyanin biosynthetic genes, but not of early biosynthetic genes. Taken together, our results provide insights on the molecular mechanisms by which the combinatorial TTG1-bHLH-MYB regulatory complexes activate and repress both developmental and biosynthetic pathways in Arabidopsis.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

No description available.

Trichomes are hair-like structures found on the surface of virtually all terrestrial plants (Yang et al., 2015). They are epidermal outgrowths that can occur on all of the aerial parts of a plant, varying markedly in size, shape, distribution, and in their ability to produce secondary metabolites. About 30% of all vascular plants carry the glandular trichomes capable of producing secondary metabolites (Glas et al., 2012). Trichomes are vitally important to plants as a defence mechanism, they are highly significant commercially, and they are of interest to plant biologists in that they serve as an excellent model system to study all aspects of plant differentiation at the single-cell level (Hulskamp, 2004). The simple, non-glandular trichomes found in Arabidopsis have been studied extensively. However the glandular trichomes of the kind found on the surface of Antirrhinum are much less well understood. The primary aim of the research reported here is to identify the gene(s) responsible for variation in epidermal hair (trichome) distribution between Antirrhinum species. Following an introduction which provides essential background on trichomes and on Antirrhinum, the thesis is presented in four parts. The first part describes a RAD-seq experiment used to produce linkage maps for the eight chromosomes making up the Antirrhinum genome and estimates the position of the Hairy gene on linkage group 8. The results are cross-validated against maps produced independently by the Xue group. It also describes novel methods developed to address a number of problems that arose during the course of the analysis, and explores the value of imputation methods in helping to overcome gaps and inconsistencies in the data. The second part presents the findings from a fine-mapping Pool-seq experiment designed to estimate the position of Hairy more precisely. The findings suggest that Hairy lies on one of a small number of scaffolds, with Scaffold 1097 being the most likely candidate. Also covered are the findings of another experiment to estimate the position of the gene that determines whether flowers are pale or dark. In this case the results indicate that the gene lies on one of a small number of scaffolds on linkage group 5. The third part presents the results of an RNA-seq experiment which, when combined with the results of the Pool-seq experiment provides evidence that Hairy might be a glutaredoxin gene on Scaffold 1097. Finally the interim results of three experiments designed to confirm that the gene identified as Hairy controls the distribution of trichomes in Antirrhinum are presented.

Glabrous Brassica napus cv Westar and very hairy AtGL3+ B. napus were transformed using Agrobacterium tumefaciens and either a full length trichome regulatory gene BnTTG1 (isoform 1 coding region called O-TTG1) or an RNAi cassette with 260 bp of a conserved region between isoform I and II (called K-TTG1), each driven by the CaMV 35S promoter. Agronomic and trichome phenotypes were observed in the resulting lines. Transformed lines developed in the glabrous Westar background showed no changes in growth or trichome density and transformation efficiency was similar to that of an empty vector control construct. Over-expression of BnTTG1 in the AtGL3+ B. napus background resulted in low transformant survival and poor seed viability, with the only surviving line O-3-7 being taller than non-transformed lines and with a completely glabrous phenotype. The two knock-down lines with the lowest BnTTG1 expression showed a dramatic increase in trichome density, with longer trichomes and expanded trichome density (up to the 12th leaf in the K-5-8 line) compared to the AtGL3+ hairy background line, which showed increased trichome density only on the first three leaves. Moreover, K-5-8 plants were healthy, with both vegetative and reproductive growth similar to that of Westar non-transgenic control plants under both greenhouse and field conditions. The relative expression of five B. napus primary trichome regulatory genes and AtGL3 was measured in three different tissues of B. napus Westar, and the AtGL3+, K-5-8 and O-3-7 transgenic lines. Over-expression of AtGL3 resulted in changes in the expression of BnGL3, BnGL2 and BnTRY. Manipulation of BnTTG1 levels also resulted in changes in expression of these three genes in addition to AtGL3. AtGL3+ plants and O-3-7 also showed increased red pigment accumulation in several above ground vegetative tissues including cotyledons, hypocotyl and leaves, whereas the K-5-8 line (knock down of TTG1) had less anthocyanin in the same tissues. The level of anthocyanin accumulation corresponded to the relative expression of the three primary anthocyanin regulatory genes BnDFR, BnANS and BnGST. In a laboratory bioassay, diamondback moth (DBM) adults (Plutella xylostella) laid more eggs on hairy leaves of K-5-8 than glabrous Westar. However, more feeding damage from young DBM larvae was observed on Westar leaves than K-5-8 in both choice and no-choice feeding assays. In a field test comparing Phyllotreta flea beetle feeding, the hairy K-5-8 leaves showed between a 30-50% reduction in feeding over four ratings on 14 to 28 day old seedlings. Curiously, the glabrous cotyledons of the two hairy lines (AtGL3+ and K-5-8) proved to be more resistant than wild type B. napus Westar cotyledons from Helix XTra® insecticide-treated or non-treated seed. These data support the introduction of AtGL3 and the knockdown of BnTTG1 to induce a dense trichome phenotype, into otherwise glabrous B. napus, resulting in an increased host plant resistance to crucifer insects, without agronomic penalties.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2006. / Härtill 4 uppsatser.