Understanding how cellulose synthesis occurs is key to understanding the formation of the plant cell wall. This understanding could also be key to modifying cellulose production to permit more efficient extraction of glucose from cellulose for the production of biobased materials. Cellulose biosynthesis is carried out by cellulose synthases; transmembrane multimeric processive glycosyltransferases responsible for polymerizing UDP‐glucose into glucan chains. Thirty‐six glucan chains bind together in parallel to form elementary cellulose microfibrils. Due to the essential nature of cellulose synthases for plant survival and the recalcitrant nature of the cell wall to chemical and enzymatic digestion, the cellulose synthases can be very difficult to analyze by traditional approaches. In an attempt to circumvent some of the issues of studying cellulose synthases, the cellulose synthase genes CESA1 and CESA3, along with the cell wall associated genes COBRA, DET3 and POM1 were recombined into an engineered Autographa californica nucleopolyhedron virus and expressed in Spodoptera fruigiperda ovarian cells. Although recombinant protein could be detected for CESA1 and CESA3, C14‐glucose incorporation on baculovirus infected cell lines have given inconclusive results to the cellulose synthase activity of the CESA1 and CESA3 proteins. With further optimization of the protein expression of CESA1 and optimization of the variability in the C14‐glucose incorporation assays, the baculovirus system may prove a useful tool for studying the cellulose synthases. / UOIT

There are a vast number of transcription factors that regulate plant growth and development. The NAC gene superfamily is one of the largest families of transcription factors in the plant kingdom. NAC gene expression profiles using Affymetrix ATH1 gene chips were obtained for different plant organs: heart embryo, mature embryo, leaf, root and flower. NAC gene expression profiles proved to be very complex, except for one NAC gene detected only in floral tissue, At1g61110. At1g61110 was shown to be specifically expressed in the anther tapetum of Arabidospis; therefore, its name was changed to TAPNAC. TAPNAC became the focus of our studies. We identified a tapnac T-DNA knockout (KO) line, SALK_069450. A molecular phenotype was observed. Several oligopeptide, sugar and metal transporters were differentially expressed. Coincidentally, a wheat NAC gene, named TaNAM-B1 for its high sequence similarity to ATNAM, TAPNAC and At3g15510 was found to be involved in nutrient remobilization. PHOSPHOLIPASE Dα1 (PLDα1) was also found to be down-regulated in the tapnac KO. PLDα1 is an enzyme which hydrolyzes phospholipids that are part of tapetal cell membranes and tapetal lipid bodies. Once these tapetal cell structures are disrupted, the secretion of the compounds that form part of the pollen coat (i.e. proteins, flavonoids and lipids) into the anther locule is facilitated. Promoter deletion analysis using a GUS reporter and later GUS immuno-localization confirmed the findings of Wellmer and others. TAPNAC is a tapetal specific gene. The cis-regulatory sequence that enhances tapetal expression in the TAPNAC promoter was identified. The consensus motif TCGTGT increased tapetal expression of a GUS reporter gene, only when flanked by the TAPNAC minimal promoter region (-217 bp to +51 bp). In summary, TAPNAC transcription factor has been characterized and data indicates that it could play a role in nutrient remobilization from the tapetum to the pollen grains, particularly during late floral stages. Also, important information on tapetal specifcation cis-regulatory sequences was discovered. The consensus motif TCGTGT, present in TAPNAC promoter, was shown to enhance tapetal expression of a GUS reporter gene.

The ability of plants to not only detect but also adjust to their environment is crucial for their survival. The genes involved in photomorphogenesis – developmental changes in response to light – and their regulation have long been of interest to researchers. While the phytochrome and cryptochrome photoreceptors have been isolated and partially characterized, the downstream components of the light signaling pathway which transmit the perceived light signals and regulate gene expression are still being discovered. A negative regulator of photomorphogenesis, DET1 (de-etiolated 1), was discovered in a mutant screen for plants that develop a light grown phenotype in the dark. DET1 is nuclear localized, but its exact function remains unknown. Two contrasting mechanisms for the role of DET1 in the regulation of gene expression have been proposed based on studies of the tomato and human orthologs of DET1. In order to reveal the mechanism and molecular context of DET1 action, suppressor mutant screens were employed to discover additional genes acting in conjunction with DET1 (designated as TED genes). In this research, new genomic methods were developed and employed to identify the genes underlying the ted1-1SD and ted2-1D suppressor mutations. A long hypocotyl QTL and suppression of the det1-1 dark grown phenotype by the Bensheim (Be-0) ecotype of Arabidopsis mapped to the HAT4 gene, a homeoboxdomain leucine-zipper transcription factor involved in shade-avoidance responses. Sequence analysis uncovered two functionally distinct alleles of HAT4 in the Be-0 alleles of HAT4 compared to the genomic standard Columbia (Col-0) ecotype. Expression analysis showed that in addition to negative autoregulation by itself, HAT4 is also negatively regulated by DET1. The ted2-1D mutation was mapped to a 57 Kbp interval on chromosome I containing three likely candidate genes. Suppression of the det1-1 phenotype by ted2-1D is overdominant which is highly unusual and typically associated with hybrid vigor or heterosis traits. The discovery of the genes underlying the ted1-1SD and ted2-1D suppressor mutations have furthered the understanding of the role for DET1 in regulation of photomorphogenesis as well as mechanisms involved in overall gene regulation during light signaling.

Thèse de doctorat : Sciences du vivant. Aspects moléculaires et cellulaires de la biologie : Strasbourg 1 : 2008. / Titre provenant de l'écran-titre. Bibliogr. 15 p.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 120-131). Also available in print.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Turnip crinkle virus; arabidopsis; thaliana; TCV; avrRpt2; avrRpm1; avrRps4; systemic acquired resistance; virulence; Avr gene; R gene; pseudomonas syringae. Includes bibliographical references (p. 60-66).

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Botany / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Botany / Master / Master of Philosophy