Function of the SPY O-GlcNAc Transferase in Gibberellin Signal Transduction

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

This research is to understand the molecular genetics of signal transduction in Arabidopsis involving gibberellins (GA), a class of phytohormones. Although several new components of the GA signal transduction pathway have been identified, the interrelationships between these components and the mechanism by which they act remain largely unknown. The function of one such component, the SPY protein, is the focus of this project. Genetic analysis suggests that SPY is a suppressor of GA signal transduction and that its loss leads to increased signal transduction. SPY mutations completely suppress the inhibition of seed germination and partially suppress the dwarfism and sterility caused by GA-deficiency. SPY may be an O-GlcNAc transferase (OGT), an enzyme which in animals catalyzes the addition of N-acetylglucosamine to specific serine and/or threonine residues of target proteins in both the cytosol and nucleus. The N-terminal half of both SPY and animal OGT contains tandemly arrayed tetratricopeptide repeats (TPRs), which presumably are involved in protein-protein interactions. Preliminary biochemical and genetic results suggest that SPY transfers GlcNAc to proteins and that SPY is part of a multiprotein complex. The goal of this work is to confirm that SPY is an OGT and that proteins with which it associates alter its subcellular localization or activity in GA signal transduction. To determine if SPY is an OGT, the structure of the GlcNAc modification made by SPY will be determined. To determine if other components of the SPY complex regulate its localization, the size and subunit composition of the complex from different cellular compartments will be determined, and the effects of different mutations will be assessed. In addition, two-hybrid screens will be used to identify proteins that interact with SPY. Future studies will characterize the proteins that make up the complex and will determine the role of these proteins in GA signal transduction. These studies will provide important information that will enhance our fundamental understanding of gibberellin action.