SPM1 encoding a vacuole-localized protease is required for infection-related autophagy of the rice blast fungusMagnaporthe oryzae

SPM1, encoding a putative subtilisin-like protease, is involved in pathogenicity of the rice blast fungus Magnaporthe oryzae, but its detailed function remains unknown. Here, we report that SPM1 encodes a vacuole-localized protease that is a critical component for autophagy during the infection process of M. oryzae. Detailed phenotypic analysis of targeted disruption mutants of SPM1 revealed that the mutants have pleiotropic defects in infection-related steps including germination, appressorium formation, host invasion and postinvasive growth, indicating the requirement of Spm1 function for the broad phase of infection. It has been shown that the Spm1 homolog of yeast functions in autophagy, the degradation machinery mediated by vacuoles, implying the involvement of Spm1 in autophagy in M. oryzae. In-gel protease activity assay of the recombinant Spm1 protein indicated that Spm1 had a protease activity. An Spm1-GFP fusion protein was detected inside vacuoles of fungal cells, indicating that Spm1 is a protease localized in vacuoles. Furthermore, degradation of putative autophagic bodies was retarded in vacuoles of the spm1 mutant. These data strongly suggest that SPM1-encoded protease functions in autophagy required for the pathogenicity of M. oryzae.