Analysis of secreted proteins of Magnaporthe grisea and the search for protein effectors

Magnaporthe grisea is a notorious pathogenic fungus that causes rice blast disease\nworldwide. Proteins secreted by the fungus are likely candidates for being effectors that\nare potentially recognized by determinants of resistance or susceptibility in host plants.\nHowever, knowledge of the role of secreted proteins of M. grisea is still limited. In this\nstudy, I identified 29 proteins that were secreted into culture filtrates from M. grisea\nstrains expressing candidate proteins. I confirmed secretion of these proteins and tested\nthem for elicitor activity on plants. Among them, I studied two groups: cell wall\ndegrading enzymes (CWDEs) and small cysteine-rich proteins. Cysteine-rich proteins\nhave been shown in other systems to function as elicitors. Initially, I expressed and\npurified proteins in M. grisea to obtain proteins by a homologous expression system.\nAlthough this was effective for a number of proteins, the need for greater amounts of\nprotein led me to express several proteins in the Pichia pastoris system. Several candidate\nproteins were purified and found to induce symptoms on rice and maize. Hypothetical\nproteins MG10424.4 and MG09998.4 were both found to have elicitor activity. Lipase\nMG07016.4 did not induce response of plants and we concluded that the lipase activity of\nMG07016.4 does not function as an elicitor. I also purified a small cysteine-rich protein,\nwhich belongs to the group of cluster 180 proteins in M. grisea, MG10732.4 from P. pastoris. It is able to cause yellowing symptoms and hydrogen peroxide production in\nplants and it might contain elicitor activity.