Poster: Plant-pathogen interactions

Abs # 504: Investigation of the Roles of Polygalacturonase-inhibiting Proteins in Plant Defense against Pathogens

Presenter:	Yang, Liya , lyyang@ucdavis.edu
Authors	Yang, Liya  (A)   Powell, Ann LT  (B)   Lurie, Susan  (C)   Labavitch, John  (A)
Affiliations:	(A): UC Davis, Pomology Department (B): UC Davis, Vegetable Crops Department (C): Volcani Institute, Postharvest Science Department, Israel

The cell wall is an early barrier against pathogen attack. Pathogens secrete polygalacturonase (PG), a homogalacturonan pectin-cleaving enzyme, early in the infection process. The enzyme reduces wall integrity, releasing pectin-derived oligosaccharides (PDOs) that may be signals. Cell wall-localized PG-inhibiting proteins (PGIPs) selectively inhibit some fungal PGs. We have shown that tomatoes expressing a pear pgip gene display reduced lesion symptoms after grey mold, Botrytis cinerea, infection. We are now investigating the way(s) that PGIP contributes to plant defense by increasing and suppressing tomato fruit pgip (t-pgip) expression. We have made sense and antisense t-pgip constructs and generated transgenic plants. Several lines with altered tPGIP levels have been identified and lines with the highest and lowest t-PGIP activity have been self-pollinated to obtain homozygous T2 progeny that will be tested for relative susceptibility to B. cinerea. We will learn if PGIP’s contribution to plant defense is related to (1) its direct inhibition of pathogen PG or/and (2) its facilitation of the production of PDO elicitors. To test the latter, we are developing gene expression markers for fruit responses to B. cinerea. Thus far we have identified at least 7 useful “defense”-related markers. Interestingly, application of PDOs from infected tomato fruits to tomato pericarp discs induced expression of these markers in the absence of the pathogen. We will examine whether PDOs extracted from tomato lines with altered t-PGIP levels are differentially active as elicitors of marker expression. As in other species, tomato PGIPs are encoded by a small gene family. The tissue-specific expression patterns and roles of the t-PGIPs in plant defense are also under investigation.