Thesis (Ph. D.)--University of North Texas, May, 2009. / Title from title page display. Includes bibliographical references.

The model plant Arabidopsis thaliana has been very successful thus far as a tool for understanding and studying the genetics of plant development. Analysis of its sequenced genome revealed the occurrence of duplicated chromosome blocks, resulting in duplicated genes. Duplicated genes, high in sequence and/or structure similarity, form gene families. One such family, of BRX-like genes, is presented in this thesis. All members contain a characteristic "BRX" domain that is required for BRX activity in planta. BRX (BREVIS RADIX), is a novel regulator of root growth in Arabidopsis. However, analyses of Arabidopsis single and double mutants with other gene family members, suggests that BRX is the only member with a dominating role in root development. Interestingly, BRXL1, although having BRX activity in the root, does not act redundantly with BRX in vivo, presumably because it is expressed at much lower levels than BRX. These two gene family members demonstrate the uncommon phenomenon of unequal genetic redundancy in plants. Another gene family member, BRXL4, although non-redundant with regards to BRX activity in the root, did display novel shoot-related phenotypes when over-expressed. In these lines the lateral shoots and hypocotyls showed increased Gravitropic Set-Point Angles resulting in the downward growth of the adult lateral shoots and a wide range of growth directions in the hypocotyls. Over-expression lines of BRXL4 also displayed seedling agravitropism. Auxin-induced transcription as monitored by the DR5::GUS reporter, is altered in these lines compared to wild-type. Additionally, hypocotyl curvature, stem bending and amyloplast localization profiles in response to a change in gravity vector, are also altered in these over-expression lines and in the brxl4 mutant compared to wild-type.

Roots are essential for plant anchorage and nutrient uptake. Although root system architecture is genetically determined, its high level of plasticity allows rapid as well as long term adaptation to the plants' environment. To confer such adaptability, favorable alleles have been selected within species to endow them with an optimized root system. The identification of such favorable alleles is therefore a central component of research in plant breeding. / In an attempt to isolate novel factors that modulate root development, we exploited natural genetic variation in the model plant Arabidopsis thaliana. Tissue culture analysis of 44 accessions led to the identification of a line, Uk-1 (Umkirch-1), whose root system differs significantly from average accessions. A short primary root and an increased number of lateral and adventitious roots are typical for the Uk-1 root system, while the average Arabidopsis root system consists of a predominant primary root and few lateral roots. The major locus responsible for the Uk-1 phenotype, BREVIS RADIX (BRX), was successfully isolated by map-based cloning. Quantitative trait locus (QTL) analysis revealed that BRX is responsible for ca. 80% of the variance of the observed primary root length difference as compared to an average control accession. / BRX controls the extent of cell proliferation and elongation in the growth zone of the root tip and is a member of a novel, small family of proteins that contain three distinct and highly conserved domains of unknown function. BRX is a low abundant, nuclear protein, which is expressed in the phloem and the pericycle at the phloem poles. BRX is also expressed in the columella. Since BRX is not expressed in the root meristem, it must affect root growth in a secondary manner, likely by modulating responses to the plant hormone auxin. / Transcriptional profiling in root tissues revealed that BRX does so by maintaining optimal expression of the brassinosteroid biosynthesis gene CPD, and thereby optimal endogenous levels of the plant hormone brassinosteroid. Further analysis identified BRX as a central component of the interdependency of brassinosteroid signaling and auxin signaling.

Thesis (M. Sc.)--Carleton University, 2005. / Includes bibliographical references (p. 102-106). Also available in electronic format on the Internet.

No description available.

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Histone H1, or linker histone, are unique histones that bind to the nucleosome to facilitate higher order chromatin structure. The linker histones, when compared to the core histones that make up the nucleosome, are poorly understood especially in plants. Linker histones are vital for plant development as well as for cell cycle regulation, sharing many qualities with animal linker histones. In this report, the first two parts introduce the current literature of H1, including result from non-plant systems, and the third section is a research proposal describing a research project to elucidate the roles of linker histones on the regulation of FLOWERING LOCUS C (FLC) in Arabidopsis thaliana. / text

No description available.

No description available.

Ponts entre les séquences d'acides nucléiques et les protéines, les ribosomes sont des composants essentiels des cellules vivantes. Composé d'ARN et de protéines ribosomiques, ils sont transportés, durant leurs biogenèses, du nucléole au cytoplasme, où ils traduisent les ARN messagers (ARNm) en protéines. Ces dernières années,  il a été montré que nombre de protéines ribosomiques étaient impliquées dans le développement d'Arabidopsis en intervenant sur la division et l'élongation cellulaire. L'impact d'un défaut de biogenèse des ribosomes sur le développement pourrait être expliqué par un effet dose, par une spécificité des ribosomes pour leur ARNm cibles ou par la multifonctionnalité de protéines ribosomiques. Les résultats obtenus montrent que REBELOTE (RBL), l'un des deux homologues chez Arabidopsis de la protéine NOC2p de levure, intervient probablement durant la biogenèse des ribosomes. Des mutations dans le gène RBL causent une gamme de phénotype de la létalité embryonnaire aux défauts de croissance (réduction de la taille de la plante, altération de la forme des feuilles...). Afin de mieux comprendre les processus contrôlés par RBL, la fonction ribosomique de RBL a été étudiée et ses interacteurs protéiques recherchés. Nous nous sommes ensuite focalisé sur les effets des mutations rbl sur la division et l'élongation cellulaire. Ce travail montre que les défauts observés aux niveaux moléculaire et cellulaire peuvent expliquer les retards de croissance des mutants rbl. / Bridges between nucleic acids sequences and proteins, ribosomes are central components and the “auletes” of living cells.  Composed of ribosomal proteins and RNA, they move during their biogenesis from the nucleolus to the cytoplasm, where they translate RNA messengers into proteins. In the past years, some mutants of ribosomal-biogenesis-related proteins have shown the importance of these proteins during cell division and Arabidopsis development. The impact of ribosomal defects on development could be explained by dose effect (which could be important for cell fitness), specificity of ribosomes for some mRNA or multifunctional ribosomal proteins (Mary E. Byrne, 2009). Here I present our work on REBELOTE (RBL), one of the two Arabidopsis homologs of the yeast NOC2 protein, which act during the ribosomal 60S subunit biogenesis. Mutations in REBELOTE gene cause a range of phenotypes, from embryo lethality to growth defects (reduced plant size, altered leaf shape…). To have a better understanding of RBL-controlled processes, we first analyzed the ribosomal function of RBL, and searched for its protein partners. Our results shows that RBL act in two different nucleolar complexes supposed to regulate 60S ribosomal subunit biogenesis. Subsequently, we focused on the effects of rbl mutations on the cell division/elongation processes. Our work shows that defects observed at molecular and cellular levels could explain the slow down of cell divisions and growth delay in rbl mutants.