Systematic assessment of the antifungal mechanism of soil fumigant methyl isothiocyanate against Fusarium oxysporum

Fusarium oxysporum is an important phytopathogenic fungus, it can be controlled by the soil fumigant methyl isothiocyanate (MITC). However, the antimicrobial mechanism of MITC against F. oxysporum, especially at the transcriptional level, is still unclear. In this experiment, the antimicrobial mechanism of MITC against F. oxysporum was investigated. Our results indicated that when F. oxysporum was exposed to 6 mg/L MITC for 12 h, the inhibitory rate of MITC on F. oxysporum was 80%. Transmission electron microscopes showed that the cell wall and membrane of F. oxysporum had shrunk and folded, vacuoles increased, and mitochondria swelled and deformed. In addition, the enzyme activity of F. oxysporum treated with MITC showed a decrease of 32.50%, 8.28% and 74.04% in catalase, peroxidase and superoxide dismutase, respectively. Transcriptome sequencing of F. oxysporum was performed and the results showed that 1478 differentially expressed genes (DEGs) were produced in response to MITC exposure. GO and KEGG analysis showed that the DEGs identified were involved in substance and energy metabolism, signal transduction, transport and catalysis. MITC disrupted cell homeostasis by influencing the expression of some key genes involved in chitin synthase and detoxification enzymes production, but F. oxysporum also protected itself by up-regulating genes involved in energy synthesis (such as upregulating acnA, CS and LSC2 in TCA). qRT-PCR data validated the reliability of transcriptome data. Our research used biochemical and genetic techniques to identify molecular lesions in the mycelia of F. oxysporum exposed to MITC, and provide valuable insights into the toxic mechanism of pathogenic fungi mediated by MITC. These techniques are also likely to be useful for rapidly screening and identifying new, environmentally-friendly soil fumigants that are efficacious against fungal pathogens.