Molecular Biology and Developmental Functions of Wall Extension Proteins (Expansins) in Plant Cell Enlargement

9317864 Cosgrove The PI's laboratory has identified and characterized two proteins ('expansins') from cucumber hypocotyl walls that appear to mediate the acid-extension response of isolated plant cell walls. This proposal outlines a five year plan to investigate the developmental functions of these proteins and to elucidate the mechanism of their action. The proposal has five major objectives. These are: a) to clone and sequence the two expansin genes from cucumbers and one expansin gene from Arabidopsis, and to identify conserved sequences that may code for the active site of the expansins; b) To analyze the spatial and temporal patterns of the expansin gene expression at the mRNA level and to relate these to developmental patterns of growth; c) To construct transgenic plants with reduced or enhanced levels of expansin expression and to analyze the resulting alterations in phenotype; d) To map the Arabidopsis gene and test whether previously identified Arabidopsis growth mutants are deficient in expansin production; e) to express an expansin gene in E. coli as a means of verifying gene identity and as source for protein for studies on isolated cell walls and living cells. %%% This study is important because it will establish the role of this novel class of proteins in plant growth. Expansins are the only wall proteins found to date that have the ability to induce extension in isolated plant cell walls. The growth response these protein mediate seems to be common in cells with cellulosic walls and it may contribute to auxin-stimulated growth. The understanding of the role of expansins and their mech anism of action will most likely lead to important discoveries of the molecular basis of plant cell wall changes during plant growth. *** { 7 < u { ! Z ! Z Z ! F { { ( Times New Roman Symbol & Arial ` ` U ' h % < 5 Dr. Geza Hrazdina Dr. Geza Hrazdina