Molecular Genetics of Ethylene-Auxin Interactions in Arabidopsis

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Intellectual Merit. Hormones are key components in the orchestration of plant responses to developmental and environmental cues. The hormone-mediated integration process, although clearly established at the physiological level, is still largely unknown at the molecular level. This project identifies and characterizes specific points of interaction between the ethylene response and auxin biosynthetic pathway in the model plant Arabidopsis thaliana. The implications of these studies expand beyond the hormone crosstalk to the largely unknown auxin biosynthetic pathway and its regulation.Three new root-specific ethylene resistant mutants have been identified (wei2, wei7, and wei8). Cloning and characterization of wei2 and wei7 uncovered an unexpected role of a and b subunits of a tryptophan biosynthetic enzyme anthranilate synthase in the regulation of auxin biosynthesis. Similarly, initial characterization of WEI8 indicates that the WEI8 protein catalyzes the conversion of tryptophan to indole-3-pyruvic acid, a key step in auxin biosynthesis for which no genetic information was available previously. WEI8 belongs to a small multigenic family of 5 members in Arabidopsis. To further dissect the role of WEI8 and WEI8-like (WEL) genes in auxin biosynthesis, to understand their regulation by ethylene, and to identify additional genetic elements in the auxin biosynthetic pathway, the following specific goals are set. 1) Determine the role of WEI8 and its closest homologues WEL1 and WEL2 in the ethylene response. 2) Determine the role of WEI8, WEL1, and WEL2 in auxin biosynthesis. 3) Identify and characterize new wei mutants. Broader Impact. Modification of plant responses to specific hormones can be utilized to improve agricultural production. These manipulations often result in collateral adverse effects due to the diversity of functions that a single hormone has during development. Understanding of how a hormone produces completely different effects dependent on the tissue, developmental and environmental conditions, etc. is, therefore, critical for the intelligent manipulation of plant production. This project will provide basic information on the genetics of auxin biosynthesis, thus enabling people to effectively control the myriad of processes regulated by auxin in plants. An important part of the funds will be dedicated to training students and postdoctoral fellows in basic, as well as applied plant biology. As part of this training, all involved personnel will be able to attend scientific meetings to become exposed to the latest advances in the field of their research and share their own findings.