Functional Analysis of Small Auxin Up-Regulated (SAUR) Genes in Arabidopsis

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Intellectual Merit: The plant hormone auxin regulates many aspects of growth and development by modulating the expression of several hundred genes. Among the most rapidly and strongly auxin-induced genes are members of the Small Auxin Up-Regulated (SAUR) gene family. Although these genes appear to be present and are highly conserved as large gene families in all plants, virtually nothing is known regarding what role, if any, they play in auxin-mediated growth and development. Using a reverse genetic approach, we have found that overexpression of members of the Arabidopsis SAUR19 family containing N-terminal tags confers numerous phenotypes indicative of perturbed auxin-mediated growth. In contrast, overexpression of untagged SAUR19 results in no obvious affects on plant growth and development. Dr. Gray's findings suggest that SAUR19 is a highly unstable protein and the addition of an N-terminal tag to SAUR19 has a stabilizing effect on the protein. Studies to date lead to the hypothesis that SAUR19 plays a crucial role in auxin-mediated cell expansion, perhaps by functioning as a regulator of auxin transport. The goal of this project is to understand the function of SAUR19 and closely related SAUR family members in auxin regulated growth. Both forward and reverse genetic strategies will be employed to elucidate SAUR19 function, characterize SAUR19 interacting proteins, and investigate the auxin transport defect of SAUR19 transgenic seedlings in relationship to known components of the auxin transport machinery.Broader Impacts: Sequence and expression analyses suggest that SAUR genes are present as large multigene families in all plants, including mosses, monocots, and dicots. Virtually nothing is known regarding the function of the SAUR genes. Since auxin plays a central role in regulating many aspects of plant growth and development, including several traits of agricultural import such as biomass, fruit set and size, and root system development, elucidation of SAUR functions is essential for understanding auxin action, and will be of broad interest. Additionally, it is expected that this work will also contribute to our understanding of the regulation of protein stability in plants and other eukaryotes. This project will provide support for one graduate student and one postdoc, both of whom will obtain broad training in genetics, molecular and cellular biological approaches. Additionally, integration of original research and undergraduate education is an integral component of this project. Dr. Paul Overvoorde and his undergraduate students at Macalester College will play vital roles in this project. Students in Dr. Overvoorde's courses will analyze the expression of SAUR genes using promoter-beta-glucuronidase reporters and will assemble this information into an online, searchable database that will be made available to the plant research community. The creation of this database will be used as a project-based learning assignment for Macalester students in computer science/bioinformatics courses taught by the co-PI and his colleague, Dr. Elizabeth Shoop. Additionally, one undergraduate student from Macalester will be selected each year to work in the Gray lab over the summer months. These students will interact closely with the PI, co-PI, and grad students and postdocs in the Gray lab where they will obtain a valuable and unique research experience in plant molecular genetics.