Extensin mRNA and protein in plant cell walls have been shown to increase in response to wounding, ethylene, pathogen infection and exposure to fungal and plant cell wall elicitors, suggesting a protective function for this cell wall protein. This project studies another cell wall protein in carrot storage roots and soybean, called p33, that also increases in wounded tissue and also plays a role in normal plant development. The recent identification of a number of proline/hydroxyproline-rich protein genes which share sequence homology with the carrot p33 sequence suggests that p33 may represent a new class of structural cell wall proteins. Promoter deletion analysis is used to identify DNA sequences which are responsible for the synthesis of p33 in wounded carrot roots. These studies will allow the cis-acting regions which modulate p33 expression in wounded tissue and allow determination of whether these same sequences are used to regulate the expression of p33 during normal plant development. Deletion analysis of specific regions of the carrot p33 sequence will be used to identify possible "domains" within the p33 protein necessary for its function and interaction with other cell wall components. These domain deletion studies will represent a new approach to identifying sequences which may be necessary for the function of structural cell wall proteins in higher plants.%%% The cell walls of higher plants are dynamic structures which undergo changes in composition and structure in relation to cell age, tissue type and environmental stimuli. Much of the analysis of the structural protein component of the cell wall has dealt with extensin, a hydroxyproline-rich glycoprotein, and the genes which encode it. This study centers on a newly discovered cell wall protein which plays a role in normal plant growth.***//
