The plant cell wall is a structural barrier to microbes, composed of a network of polysaccharides such as cellulose, hemicellulose and pectin. During infection, the host cell wall must be degraded, a feat that is accomplished through an array of microbe-encoded Cell Wall Degrading Enzymes (CWDE). The polygalacturonases (PGs) are among the first CWDE secreted by pathogens to facilitate invasion, release of nutrients and support pathogen growth. PGIPs (polygalacturonase-inhibiting proteins) are plant cell wall proteins that specifically modulate the activity of PGs, and hamper the invasion process by limiting the host tissue colonization. The PG–PGIP interaction retards pectin hydrolysis and favors the accumulation of oligogalacturonides (OGs) leading to plant defense activation. Here we investigate the role of PGs in the oomycetes Phytophthora nicotianae and Phytophthora capsici on tobacco and tomato plants. We performed phylogenetic analyses tocharacterise PG families in the two oomycetes and, the infection assays carried out on plants expressing PGIP2 fromP. vulgaris. Finally we present our latest results studying PG effector function in Phytophthora during the infection cycle.
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