Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 128-129). Also available on the Internet.

No description available.

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

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