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.

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

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 4 uppsatser.

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

Thesis (Ph. D.)--University of Oregon, 2000. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 50-54). Also available for download via the World Wide Web; free to University of Oregon users. Address: http://wwwlib.umi.com/cr/uoregon/fullcit?p9963440.

Thesis (M.A.)--York University, 2007. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 53-63). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR31999

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published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Apyrases are proteins that bind to and hydrolyze most nucleoside di- and triphosphates, but not nucleoside monophosphates. Some function inside the cell; others hydrolyze extracellular nucleotides in the extracellular matrix. In Arabidopsis, apyrases and eATP have been implicated in diverse responses, ranging from phosphate mobilization to herbicide and toxin resistance to overall plant growth. Isolated garden pea nuclei exhibit phytochrome-dependent, red/far red-reversible changes in apyrase activity and in protein phosphorylation. O-linked β-N-acetylglucosamine (O-GlcNAc) is a post-translational modification that functions in a manner analogous but often antagonistic to O-phosphorylation. Given the known red light effects in pea nuclei and the link between O-GlcNAc and O-phosphorylation, we tested whether O-GlcNAc modification in pea nuclei might change in response to red light (Rc). Western blots showed that anti-O-GlcNAc antibody could sometimes recognize modifications in pea nuclei proteins, but not consistently. Experiments testing red light irradiation, O-GlcNAc transferase inhibitors, and GlcNAcase inhibitors all yielded similarly inconsistent results. As the project progressed we learned that the O-GlcNAc modification is very labile, and that this lability was the probable basis of the inconsistent results. Methods to overcome this technical problem were not readily available and so this project was not pursued further. A second project focused on identifying the members of the protein complexes associated with apyrase in partially purified nuclear preparations. The apyrase complex was isolated from etiolated seedlings of both Arabidopsis and pea by co-immunoprecipitation using antibodies raised against purified protein from each system. Apyrase activity was also compared in etiolated and red-light irradiated nuclei in both systems. For both experiments and in both systems, the complex of proteins associated with apyrase in etiolated and Rc-irradiated nuclei were not consistently different. The discovery of a cotton EST with a sequence similar to other plant apyrases opened a new line of investigation in a model system with fibers that are suited for the study of growth kinetics of single cells. This putative apyrase is expressed at high levels in elongating fibers but not in fibers that are not elongating or in ovules, suggesting that apyrase may influence cotton fiber elongation. Studies of fiber growth kinetics in the presence of inhibitors that block apyrase activity, chemical inhibitors of animal P2X-type purinoceptors, and anti-apyrase antibodies also favor this hypothesis. I cloned the full length cDNAs of GhApy1 and GhApy2. Antibodies raised against a suspected antigenic and variable sequence of GhApy1 were produced and confirmed to recognize native cotton apyrase. Crude protein isolated from pollen exhibited apyrase activity. / text