Role of <i>FoERG3</i> in Ergosterol Biosynthesis by <i>Fusarium oxysporum</i> and the Associated Regulation by <i>Bacillus subtilis</i> HSY21

Abstract

Ergosterol is an important component of the fungal cell membrane and represents an effective target of chemical pesticides. However, the current understanding of ergosterol biosynthesis in the soybean root rot pathogen <i>Fusarium oxysporum</i> remains limited. In addition, the regular use of fungicides that inhibit ergosterol synthesis will seriously harm the ecological environment and human health. <i>Bacillus subtilis</i> is gradually replacing chemical control as a safe and effective biological agent; to investigate its effect on ergosterol synthesis of <i>F. oxysporum</i>, we verified the biological function of the <i>FoERG3</i> gene of <i>F. oxysporum</i> by constructing knockout mutants. The results showed that knocking out <i>FoERG3</i> blocked ergosterol biosynthesis, restricted mycelial growth, and increased the sensitivity to external stressors (NaCl, D-sorbitol, Congo Red, and H₂O₂). The increased permeability of the cell membrane promoted increased extracellular K⁺ levels and decreased mitochondrial cytochrome C contents. Treatment with suspension of <i>B. subtilis</i> HSY21 cells resulted in similar damage as observed when treating <i>FoERG3</i>-knockout <i>F. oxysporum</i> cells with ergosterol, which was characterised by deformity and swelling of the mycelium surface; increased membrane permeability; decreased pathogenicity to soybeans; and significantly decreased activities of cellulase, β-glucosidase, amylase, and pectin-methyl galactosylase. Notably, deleting <i>FoERG3</i> resulted in a significant lag in the defense-response time of soybeans. Our results suggest that <i>FoERG3</i> strongly influences the virulence of <i>F. oxysporum</i> and may be used as a potential antimicrobial target by <i>B. subtilis</i> HSY21 to inhibit ergosterol synthesis, which supports the use of <i>B. subtilis</i> as a biological control agent for protecting against <i>F. oxysporum</i> infection.