Arabidopsis 2010: Systematic Discovery of Ligands for Arabidopsis START proteins

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Intellectual merit. Plant growth is controlled in part by small molecule signals called hormones. These hormones work by binding to receptor proteins, which in turn function to coordinate responses like gene transcription and cellular growth. For example, the hormone abscisic acid (ABA) is a small lipophilic compound that is synthesized by plants in times of stress. Once synthesized, it binds to a receptor protein, which in turn inhibits growth and activates the transcriptional responses needed for acclimation to stressful environmental conditions. Numerous hormone-receptor pairs have been defined and are known to control many aspects of plant growth. Thus, hormone signals and their receptor proteins are a central preoccupation of modern plant biological studies. With complete genome sequences in hand, it is apparent that the genomes of higher plants encode hundreds more receptor proteins than known hormones; this and other observations imply that more hormones exist than we currently know about. Given the well-documented importance of plant hormones, new methods and tools for discovering hormones may have a transformative influence on our understanding of plant biology.In principle, one way to identify hormones is to purify them by virtue of their association with their receptor proteins. To develop, explore and implement this idea, this project will execute a simple and general strategy for identifying compounds that bind to receptor proteins. The project focuses on START proteins, which form a large family of known or suspected hormone receptors. The Arabidopsis genome encodes 89 START proteins, several of which play important roles in developmental, abiotic or biotic stress biology. In spite of their importance, the endogenous ligands for most START proteins are not known. In this project, we leverage recent technological advances in protein-ligand identification to systematically characterize the ligands of Arabidopsis START proteins. Using recently developed small-molecule pull down methods, we will use START proteins as reagents that guide the identification and subsequent purification of their endogenous ligands. Once isolated, the structure of these ligands will be determined using a combination of high-sensitivity microprobe 2D-NMR and other methods. Our proposal rests on an integrative base of diverse approaches and builds a robust foundation for a new wave of protein-targeted ligand discovery, which will enable the discovery of new hormones.Broader impacts This interdisciplinary project will provide students and post-docs an internationally unique training environment for plant chemical biology and genetics. In addition, through UCR?s REU program and other avenues, undergraduates, including underrepresented minorities will be trained in methods for metabolite analysis, purification, isolation and general plant biology. The PI maintains a website that provides information and technical advice about plant chemical genomics and chemical biology. This site is gateway to information about the laboratory's chemical resources that the PI has shared with dozens of laboratories across the world. Protocols for small molecule pull downs and metabolite purification will be made publicly available and disseminated through the PI's website. This project, which will systematically define protein-metabolite interactions for an entire protein family, is unprecedented in any organism and will create an exciting, interdisciplinary training environment that produces scientists ready to embrace the challenges associated with adopting new approaches to important biological questions. The discovery of new hormones and growth regulators is additionally expected to be of long-term benefit to agriculture.