Comparative Secretome Analysis of Magnaporthe oryzae Identified Proteins Involved in Virulence and Cell Wall Integrity

Plant fungal pathogens secrete numerous proteins into the apoplast at the plant–fungus contact sites to facilitate colonization.However,only a few secretory proteins were functionally characterized in Magnaporthe oryzae,the fungal pathogen causing rice blast disease worldwide.Asparagine-linked glycosylation 3(Alg3)is an a-1,3-mannosyltransferase functioning in the Nglycan synthesis of N-glycosylated secretory proteins.Fungal pathogenicity and cell wall integrity are impaired inΔalg3 mutants,but the secreted proteins affected inΔalg3 mutants are largely unknown.In this study,we compared the secretomes of the wild-type strain and theΔalg3 mutant and identified 51 proteins that require Alg3 for proper secretion.These proteins were predicted to be involved in metabolic processes,interspecies interactions,cell wall organization,and response to chemicals.Nine proteins were selected for further validation.We found that these proteins were localized at the apoplastic region surrounding the fungal infection hyphae.Moreover,the Nglycosylation of these proteins was significantly changed in theΔalg3 mutant,leading to the decreased protein secretion and abnormal protein localization.Furthermore,we tested the biological functions of two genes,INV1(encoding invertase 1,a secreted invertase)and AMCase(encoding acid mammalian chinitase,a secreted chitinase).The fungal virulence was significantly reduced,and the cell wall integrity was altered in theΔinv1 andΔamcase mutant strains.Moreover,the N-glycosylation was essential for the function and secretion of AMCase.Taken together,our study provides new insight into the role of N-glycosylated secretory proteins in fungal virulence and cell wall integrity.