The auxins are an important class of plant hormones involved in many aspects of plant development The most common naturally occurring auxin is indole-3-acetic acid, or IAA. In Arabidopsis, up to 95% of the IAA pool is found conjugated to small molecules such as sugars and amino acids. However, the genes and enzymes involved in IAA conjugate metabolism are not yet well understood. A mutant, iar1, that is resistant to the inhibitory effects of multiple IAA-amino acid conjugates on root elongation was identified. The IAR1 gene encodes a protein with numerous transmembrane domains and several histidine-rich regions. The IAR1 protein has homologs in other organisms, including Drosophila, C. elegans, and mammals, and is similar in molecular structure to the ZIP family of zinc transporters from Arabidopsis and yeast. Plant reproduction requires precise control of the transition to flowering in response to environmental cues. We have isolated a late-flowering Arabidopsis mutant, fkf1, that is rescued by vernalization or gibberellin treatment. The mutant also exhibits a light-dependent hypocotyl elongation defect. We used a positional approach to clone FKF1, which encodes a novel protein with an N-terminal PAS domain similar to the flavin-binding region of certain photoreceptors, an F-box motif characteristic of proteins that target ubiquitin-mediated degradation, and six kelch repeats predicted to fold into a beta-propeller. FKF1 mRNA levels oscillate with a circadian rhythm and the fkf1 deletion mutation alters the rhythmic expression of other clock-regulated genes, implicating FKF1 in regulation of the circadian clock.

Auxin is an important plant hormone that plays significant roles in plant growth and development, influencing apical dominance, hypocotyl elongation, lateral root initiation, gravitropism, and phototropism. There are two forms of endogenous auxin, indole-3-butyric acid (IBA) and the more abundant indole-3-acetic acid (IAA). Auxin signal transduction pathways remain to be fully elucidated, though numerous auxin-response mutants have been identified. IBR5 is a gene potentially involved in auxin signal transduction. The ibr5 mutant has pleiotropic defects including decreased sensitivity to the inhibitory effects of auxin, synthetic auxins, auxin transport inhibitors, and the phytohormone abscisic acid. Like certain other auxin-response mutants, ibr5 has a long root and short hypocotyl when grown in the light. Additionally, ibr5 displays aberrant vascular patterning, increased leaf serration, and reduced accumulation of an auxin-inducible reporter. Positional information was used to determine that the gene defective in ibr5 encodes an apparent dual-specificity phosphatase. Using immunoblot and promoter-reporter gene analyses, we found that IBR5 is expressed throughout the plant. The identification of IBR5 relatives in other flowering plants suggests that IBR5 function is conserved throughout angiosperms. The results suggest that IBR5 is a phosphatase modulating phytohormone signal transduction and support a link between auxin and abscisic acid signaling pathways. Less is known concerning IBA function, though this auxin is widely used for rooting in commercial and agricultural settings. IBA functions primarily via its conversion to IAA by a process similar to fatty acid beta-oxidation in the peroxisomes. Additionally, IBA may act via its own signaling pathway, separate from IAA. Screens for mutants resistant to the inhibitory effects of IBA that remain sensitive to IAA have revealed 32 mutants to date. These IBA-response mutants have been placed into five distinct classes based on phenotypic analyses of root and hypocotyl elongation following growth on various hormones and unsupplemented medium. Here I characterize eight IBA-response mutants and use positional information to localize the genes defective in these mutants. Analyzing genes involved in IAA and IBA responses will provide a better understanding of the function of auxin in Arabidopsis thaliana and may eventually allow manipulation of the pathways involved to enhance agricultural production.

Catharanthus roseus, a tropical plant, produces the valuable anti-cancer compounds, vincristine and vinblastine in extremely low amounts. My research objectives were to examine the response of plant secondary metabolism to various metabolic perturbations, and indicate limitations in the reaction network. In hairy roots, tabersonine is an important intermediate in the synthesis of vindoline, a monomer in the formation of the anti-cancer compounds that are generally absent from cell and hairy root cultures. To understand how much metabolic flux is directed toward the tabersonine branchpoint, transient profiles of lochnericine and horhammericine in relation to tabersonine in both dark and light-adapted cultures were quantified. The results demonstrated that the accumulation of lochnericine was growth related, similar to tabersonine, and that light repressed the formation of all three alkaloids. Using enzyme inhibitors, the involvement of separate P-450 mononoxygenase dependent enzymes in the biosynthesis of horhammericine and lochnericine was demonstrated. Furthermore, horhammericine and lochnericine were observed to be turned over. A search for rate limiting regions of the pathway was accomplished through precursor feeding studies. By identifying precursors, which after feeding, significantly enhance the production of alkaloids, the specific precursor branch that is limiting flux to alkaloids can be elucidated. Precursors fed from the terpenoid portion of the pathway at 21 days in the culture cycle were found to enhance the specific yield of tabersonine. This result suggests that during the early stationary phase period (21--24 days) flux limitations may occur upstream of geraniol. On the other hand, the rate-limiting pathway could not be identified during the late growth phase (17--21 days). In part, this was due to the fact that tryptophan served as a precursor of indole acetic acid (IAA), a plant growth regulator. Therefore, changes in indole alkaloid accumulation and root growth due to tryptophan feeding were similar to those induced by exogenously added IAA. Since feeding tryptamine or terpenoid precursors did not significantly enhance indole alkaloid accumulation the rate-limitation may be downstream of loganin. The metabolic flux distribution between separate alkaloid branches was quantified by monitoring the transient profiles of multiple alkaloids. The flux towards the Iboga alkaloids decreased while the flux to the Aspidosperma alkaloids increased between 12 and 26 days. In contrast, the flux distribution between the Corynanthe branch and the sum of the Iboga and Aspidosperma branches remained unchanged during this period. Despite significant changes in extracellular nutrient levels during this period, the total flux to the alkaloids remained constant between 12 and 26 days. Through the precursor feeding and biogenetic flux analysis studies, flux limitations to alkaloids likely exist in the terpenoid pathway leading to secologanin. With the tools developed to quantify metabolic flux through a simple model, metabolic flux in metabolically engineered plant cell and tissue cultures can be routinely analyzed.

Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2007. / Source: Dissertation Abstracts International, Volume: 68-09, Section: B, page: 5744. Adviser: Mark Estelle. Title from dissertation home page (viewed May 9, 2008).

Thesis (Ph.D.)--University of Hawai'i at Manoa, 2005. / (UnM)AAI3198363. Source: Dissertation Abstracts International, Volume: 66-12, Section: B, page: 6430. Chair: Dulal Borthakur.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-06, Section: B, page: 3461. Adviser: Nicki J. Engeseth. Includes bibliographical references (leaves 173-211) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 0745. Adviser: German Bollero. Includes bibliographical references (leaves 172-181) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 2984. Adviser: David F. Clayton. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2008. / Title from PDF t.p. (viewed on Feb. 17, 2010). Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7343. Adviser: Mark Estelle.

Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2005. / Source: Dissertation Abstracts International, Volume: 66-06, Section: B, page: 2998. Adviser: Roger P. Hangarter. "Title from dissertation home page (viewed Dec. 4, 2006)."