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

摘要

Magnaporthe grisea is a notorious pathogenic fungus that causes rice blast diseaseworldwide. Proteins secreted by the fungus are likely candidates for being effectors thatare potentially recognized by determinants of resistance or susceptibility in host plants.However, knowledge of the role of secreted proteins of M. grisea is still limited. In thisstudy, I identified 29 proteins that were secreted into culture filtrates from M. griseastrains expressing candidate proteins. I confirmed secretion of these proteins and testedthem for elicitor activity on plants. Among them, I studied two groups: cell walldegrading enzymes (CWDEs) and small cysteine-rich proteins. Cysteine-rich proteinshave been shown in other systems to function as elicitors. Initially, I expressed andpurified proteins in M. grisea to obtain proteins by a homologous expression system.Although this was effective for a number of proteins, the need for greater amounts ofprotein led me to express several proteins in the Pichia pastoris system. Several candidateproteins were purified and found to induce symptoms on rice and maize. Hypotheticalproteins MG10424.4 and MG09998.4 were both found to have elicitor activity. LipaseMG07016.4 did not induce response of plants and we concluded that the lipase activity ofMG07016.4 does not function as an elicitor. I also purified a small cysteine-rich protein,which 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 inplants and it might contain elicitor activity.