Function of Arabidopsis thaliana Proline Rich Proteins in Root Hairs and Guard Cells of Arabidopsis

University Of Vermont & State Agricultural College, Burlington VT

Investigators

Abstract

The plant cell wall is a dynamic structure that can be modified in response to developmental and environmental signals. In this manner, the cell wall provides structural information that helps maintain cellular form and function during plant growth. The structure of the cell wall also changes in response to pathogen infection and stresses, such as drought, high salt and cold temperature, in a manner that helps protect plants from biotic and abiotic stresses when grown in natural environments. Expression of many of the structural proteins in the wall have been shown to be cell-type specific, suggesting that these proteins play novel roles in modifying cell wall structure in order to provide mechanical strength and assist in proper wall assembly. Proline-rich proteins (PRPs) represent an integral family of structural cell wall proteins whose expression has been linked to active growth in a number of plant systems. We have used a combination of PRP promoter/GUS fusions and epitope-tagging to characterize the expression of these genes in arabidopsis and their localization to the walls of specific cell types. Two of these proteins, AtPRP1 and AtPRP3, are expressed during the early stages of root hair outgrowth but are localized within different regions of the root hair cell wall. These results suggest that individual PRP gene family members may play distinct roles in helping to establish root hair cell wall structure during wall assembly. In addition, we have shown that AtPRP4 is expressed in guard cells and localizes to the inner shelf of the guard cell wall. We have isolated several T-DNA insertion alleles for these three proteins and we propose to characterize the loss-of-function phenotypes in these mutants associated with root hair and guard cell function. In addition, we will examine the ability of epitope-tagged PRP sequences to become cross-linked within the wall in wild type and mutant PRP backgrounds. In combination, these experimental approaches should provide new insight into the nature of the amino acid sequences encoded within individual AtPRPs that are sufficient for their targeted localization within the cell wall and their insolubilization within the extracellular matrix. Identification of the function of structural cell wall proteins in defining cell-type specific matrix structures is an important first step in our ability to modify the cell walls of plants in a manner that will let them grow in adverse environments. We have shown that the AtPRP proteins participate in determining cell wall structure in guard cells and root hairs, two cell types that are crucial for nutrient uptake and maintenance of water balance during growth. Further analysis of the function of these proteins may allow us to devise novel mechanisms for enhancing plant growth under conditions of water and/or nutrient limitation.