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INVESTIGATOR: Westfall, C. S.

PERFORMING INSTITUTION:
Washington University
One Brookings Drive
St Louis, MISSOURI 63130-4862

STRUCTURE AND FUNCTION OF THE RICE GH3 ENZYME FAMILY: REGULATING PLANT HORMONE ACTIVITY

NON-TECHNICAL SUMMARY: Plants have the ability to detect a wide range of different environmental cues and adapt their metabolism to maximize survival and reproduction. Small molecules called hormones are responsible for the movement of this signal from the cue sensing cells to the entire plant system. These hormones play a role in almost every pathway in the plant. The hormone pathways involved in disease resistance, drought resistance, growth, and seed development have been the most studied in the hopes of creating better crop plants. The activity of any hormone is dependent on the amount present in the plant and whether any molecules (such as sugars or amino acids) are attached to the hormone. This allows the plant to tightly regulate the activity of any hormone through multiple methods. The GH3 family of enzymes is responsible for attaching amino acids to a variety of different hormones. GH3-mediated conjugation can lead to activation, inactivated storage, or degradation of the hormone. So far, only a few GH3 proteins have been studied and their hormone-amino acid preference determined. This project aims to study how the GH3 proteins recognize their hormone and amino acid substrates and how GH3 sequence leads to the hormone-amino acid preference. Understanding the role between GH3 sequence and function will allow the extrapolation of GH3 function to unstudied GH3 proteins in sequenced crop plants and help lay the groundwork for future studies in these crop plants.

OBJECTIVES: Hormone conjugation is a key regulatory element of multiple plant signaling pathways. The GH3 family of proteins is responsible for the conjugation of amino acids to a variety of hormones, controlling their activity. Our objectives are (1) to determine the substrate specificity for the majority of the GH3 family in rice and Arabidopsis thaliana; (2) to determine the crystal structure of various GH3 proteins to determine the key residues for substrate recognition; and (3) to extend this knowledge to unstudied GH3 proteins in sequenced crop plants by predicting substrate specificity from sequence alone.