A study on the role of catalase from Magnaporthe grisea and an inhibitor of catalase from rice cells in the rice-blast

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In order to develop a novel experimental system to analyze the molecular mode of interaction between rice cells (Oryza sativa cv. Nipponbare) and rice blast fungus (Magnaporthe grisea), suspension-cultured cells of rice were co-cultured with conidia suspension of various field isolates of the rice blast fungus and analyzed defense responses by rice including the production of H_2O_2 and expression of defense-related genes. The level of H_2O_2 was higher when co-cultured with incompatible fungal isolates than with compatible ones. The difference was due not to the gene-for-gene relationship but to the activity of catalase found in the conidia suspension, the level of which was specific to each isolates. In the leaf sheath assay for up to 48 h, inoculation with both compatible and incompatible spores washed to remove catalase activity resulted in a significant reduction in invasion. The addition of catalase to the washed spore suspension increased the efficiency of invasion. The removal or addition of catalase in the spore suspension was related to the level of accumulated H_2O_2 in the infected leaf cells as observed by staining with diaminobenthidine. In the leaf blade assay, inoculation of washed compatible spores formed smaller lesions than washed spores with added catalase at 5 days. These results suggested that fungal catalase is a pathogenesis-related factor in the rice blast fungus. Similar catalase activities were detected in the culture filtrate of the fungus, and the enzyme was partially purified from the culture filtrate by gel filtration, DEAE-cellulose column chromatography and SDS-polyacrylamide gel electrophoresis. Analysis of the endogenous amino acid sequences after digestion of the protein with protease showed that the H_2O_2-degrading activity is carried by a catalase/peroxidase that is specifically found in eukaryotic microbes. In Magnaporthe grisea, a single-copied gene encodes the enzyme.