Decapeptide Inducer Promotes the Conidiation of Phytopathogenic Magnaporthe oryzae via the Mps1 MAPK Signaling Pathway

Magnaporthe oryzae(M. oryzae) is a phytopathogenic fungus that inflicts damage on vital crops, particularly rice. Its asexual reproduction leads to the generation of numerous conidia, which is a critical factor contributing to the prevalence of rice blast disease. However, the molecules regulating the asexual reproduction ofM. oryzaeare unknown. In our study, to identify the molecules capable of regulating the asexual reproduction ofM. oryzae, compositions of the complete medium (CM) were screened. Results showed that acid-hydrolyzed casein (AHC) could remarkably promote conidial production. OneM. oryzaeconidiation inducer was isolated from AHC using high-performance liquid chromatography (HPLC) under the guidance of bioassay. Its structure was further elucidated as a decapeptide compound (pyroGlu-EQNQEQPIR) by LC-MS/MS, chemical synthesis, and conidium-inducing assays, namedM. oryzaeconidiation inducer decapeptide (MCIDP). MCIDP could significantly promote the conidiation ofM. oryzaeand two other filamentous ascomycetes (Botrytis cinereaandFusarium graminearum). The Mps1 MAPK cascade signaling pathway is crucial for conidiation, and the effect of MCIDP on this pathway was investigated to elucidate the mechanism underlying conidiation enhancement. qRT-PCR analysis demonstrated that MCIDP could remarkably upregulate the gene expression within the Mps1 MAPK cascade signaling pathway, especially theWSC2,WSC3,PKC1,MKK1,MPS1,andMIG1. Furthermore, the ΔMowsc1, ΔMowsc2, ΔMowsc3, and ΔMomid2mutant strains were constructed. Bioassay results showed that MCIDP failed to promote conidial formation and hyphal growth in these mutant strains. These findings indicate that MCIDP promotes conidiation ofM. oryzaeby modulating the Mps1 MAPK signaling pathway.