Insights into the mechanism of Sub3 inhibiting Fusarium moniliforme infection in maize

Fusarium moniliforme (F. moniliforme) and its secondary metabolite fumonisin pose a severe threat to food safety, and searching for effective antimicrobial agents is a focus of current research. In this study, the secondary structure of Sub3 was analyzed by circular dichroism, meanwhile, the inhibition rate of Sub3 against spores, mycelia of F. moniliforme and infected maize was studied. To explore the possible inhibition mechanisms, morphological and structural changes of spores treated with Sub3 at 0, 1/2MIC (minimum inhibitory concentration) and MIC were observed by scanning electron microscopy and transmission electron microscopy; the cell wall integrity, membrane integrity, reactive oxygen species, mitochondrial membrane potential, ATP synthase activity, redox reactions, and the nuclear damage of F. moniliforme were also investigated. The results showed that Sub3 was mostly in the state of random in deionized water, while mainly showed the β-sheet structure in the hydrophobic environment of 50% Trifluoroethanol (TFE) solution, indicating that Sub3 might generate partial structure deformation when acting on the cell membrane; and its MIC on F. moniliforme spores was 0.2 g/L. Under the 1/2MIC and MIC, the inhibition rates of Sub3 against F. moniliforme infected maize were 34.3% and 75.6%, respectively. The results of inhibition mechanisms revealed that the defective pathogenicity of F. moniliforme caused by Sub3 was attributed to damages on both the cell wall and the cell membrane, which might upset balance of intracellular redox system and mitochondrial energy metabolism and trigger nucleus damage, ultimately leading to cell death. Meanwhile, Sub3 could diminished ATP synthase enzyme activity in a dose-dependent manner. The results provided direct evidence for inhibition of F. moniliforme infection of maize by Sub3, and useful knowledge applicable for food preservation.