Molecular Diversification of Plant Hormone Modification by Acyl Acid Amido Synthetases

Washington University, Saint Louis MO

Investigators

Abstract

Plants need to respond to their surroundings and changes in their environment. To do that, plants use various hormones to control how they grow under normal and stress conditions, such as drought, nutrient starvation, sunlight changes, and attack by pests and pathogens. These small molecules also influence crop productivity. The intricate systems that link small molecule hormones to developmental changes in plants are just beginning to be understood. One way of controlling responses to plant hormones is to alter the chemical structure of the hormone; this provides a molecular on/off switch. This project focuses on a family of plant proteins that modify plant hormones to turn them on and off and will use newly identified route for altering levels of the major plant hormone auxin. Understanding how plants control their growth and development, especially to improve their ability to survive under stress conditions, is essential for improving crop yields and for meeting the potential of a bio-based economy in the future. This project will also provide an interdisciplinary training environment for scientists at all levels from postdoctoral researchers to high school students that combines experimental approaches from structural biology, biochemistry, and plant biology. The integration of pre- and post-receptor metabolic and signaling pathways controls hormone responses for plant growth and development. Metabolism and localization of auxin during plant development is critical for establishing active hormone responses and biological effects. As part of the system that regulates plant hormones, GH3 acyl acid amido synthetases control levels of major plant hormones, including jasmonic acid and auxin, and modulate pathways responsible for plant growth and development, seed development, light signaling, drought response, and pathogen resistance. Biochemically, the GH3 proteins catalyze the conjugation of amino acids to acyl acids to regulate levels of active and inactive forms of jasmonates and auxins. Diversification of acyl acid substrate specificity in this enzyme family allows for alteration of metabolites in biosynthetic pathways beyond jasmonate and indole acetic acid, such as the endogenous auxin indole-3-butyric acid (IBA), and for the modification of synthetic auxins, which suggests possible uses in herbicide tolerance mechanisms. This project will determine the role of an IBA-specific Gretchen Hagen (GH3) protein in plant seedling growth, investigate the molecular basis of GH3 protein specificity for different auxins and evaluate the modification of phenoxyalkanoic acids by GH3 proteins as an herbicide tolerance mechanism. This project is supported by the Molecular Biophysics Cluster of the Molecular and Cellular Biosciences Division in the Directorate for Biological Sciences.