Function of the Small Hsps in Stress Tolerance, Growth and Development

University Of Arizona, Tucson AZ

Investigators

Abstract

The long term goal of the proposed research is to define plant small heat shock protein (sHsp) function at both physiological and mechanistic levels. sHsps are a ubiquitous group of stress proteins that are believed to act as molecular chaperones to prevent irreversible denaturation/aggregation of other proteins. sHsp chaperone function is potentially critical to plant survival of many different kinds of stress and to specific stages of plant growth and development. Plants are characterized by an unusual complexity of proteins belonging to the sHsp family; plants express both multiple cytosolic sHsps and specific sHsp isoforms targeted to intracellular organelles. The evolutionary expansion of the sHsp family in plants indicates that sHsps have provided a selective advantage over time in many contexts. The complete definition of the sHsp family from Arabidopsis, along with the biochemical framework from our studies of sHsp structure and chaperone action in vitro, provide a new starting point for investigations of sHsp function. Using a combination of molecular genetic and biochemical approaches in Arabidopsis thaliana we will define the physiological role of specific sHsps in stress tolerance, growth and development, and identify specific sHsp substrates. The proposed research has three specific aims. Aim 1: To determine the growth and stress tolerance phenotypes of sHsp loss- and gain-of-function plants. RNA interference transgenics and/or T-DNA insertional mutants for genes representing the class I & II cytosolic sHsps, as well as plants constitutively expressing class I and/or II sHsps, will be characterized for growth and stress tolerance. Aim 2: To identify potential sHsp substrates. We will test the hypothesis that sHsps bind a wide range of protein substrates and that each sHsp class interacts with unique substrates. Aim 3: To define other biochemical phenotypes of sHsp loss-of-function mutants. With these experiments it will finally be possible to test long-standing hypotheses about the importance of sHsps to plant stress tolerance and development and to uncover new functions for these unique chaperones.