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

<i>Magnaporthe oryzae</i> (<i>M. oryzae</i>) 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 of <i>M. oryzae</i> are unknown. In our study, to identify the molecules capable of regulating the asexual reproduction of <i>M. oryzae</i>, compositions of the complete medium (CM) were screened. Results showed that acid-hydrolyzed casein (AHC) could remarkably promote conidial production. One <i>M. oryzae</i> conidiation 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, named <i>M. oryzae</i> conidiation inducer decapeptide (MCIDP). MCIDP could significantly promote the conidiation of <i>M. oryzae</i> and two other filamentous ascomycetes (<i>Botrytis cinerea</i> and <i>Fusarium graminearum</i>). 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 the <i>WSC2</i>, <i>WSC3</i>, <i>PKC1</i>, <i>MKK1</i>, <i>MPS1,</i> and <i>MIG1</i>. Furthermore, the Δ<i>Mowsc1</i>, Δ<i>Mowsc2</i>, Δ<i>Mowsc3</i>, and Δ<i>Momid2</i> mutant 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 of <i>M. oryzae</i> by modulating the Mps1 MAPK signaling pathway.