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Identification of Cell Wall-Associated Proteins from Phytophthora ramorum

¹Laboratory of Phytopathology, Plant Sciences Group, Wageningen University, Binnenhaven 5, NL-6709 PD Wageningen, The Netherlands; ²Swammerdam Institute for Life Sciences, University of Amsterdam, Nieuwe Achtergracht 166, NL-1018 WV Amsterdam, The Netherlands

The oomycete genus Phytophthora comprises a large group of fungal-like plant pathogens. Two Phytophthora genomes recently have been sequenced; one of them is the genome of Phytophthora ramorum, the causal agent of sudden oak death. During plant infection, extracellular proteins, either soluble secreted proteins or proteins associated with the cell wall, play important roles in the interaction with host plants. Cell walls of P. ramorum contain 1 to 1.5% proteins, the remainder almost exclusively being accounted for by glucan polymers. Here, we present an inventory of cell-wall-associated proteins based on mass spectrometric sequence analysis of tryptic peptides obtained by proteolytic digestion of sodium dodecyl sulfate-treated mycelial cell walls. In total, 17 proteins were identified, all of which are authentic secretory proteins. Functional classification based on homology searches revealed six putative mucins or mucin-like proteins, five putative glycoside hydrolases, two transglutaminases, one annexin-like protein, the elicitin protein RAM5, one protein of unknown function, and one Kazal-type protease inhibitor. We propose that the cell wall proteins thus identified are important for pathogenicity.

Additional keywords: cell wall proteome .