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.
Melatonin is a low-cost natural small indole molecule with versatile biological functions. However, melatonin's fungicidal potential has not been fully exploited, and the mechanism remains elusive. Here, we report that melatonin broadly inhibited 13 plant pathogens. In the rice blast fungal pathogen Magnaporthe oryzae , melatonin inhibited fungal growth, formation of infection-specific structures named appressoria, and plant infection, reducing disease severity. Melatonin entered fungal cells efficiently and colocalized with the critical mitogen-activated protein kinase named Mps1, suppressing phosphorylation of Mps1. Melatonin's affinity for Mps1 via two hydrogen bonds was demonstrated using surface plasmon resonance and chemical modifications. To improve melatonin's efficiency, we obtained 20 melatonin derivatives. Tert-butyloxycarbonyl melatonin showed a 25-fold increase in fungicidal activities, demonstrating the feasibility of chemical modifications in melatonin modification. Our study demonstrated the broad-spectrum fungicidal effect of melatonin by suppressing Mps1 as one of the targets. Through further systematic modifications, developing an eco-friendly melatonin derivative of commercial values for agricultural applications appears promising.
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