Erg4 Is Involved in Ergosterol Biosynthesis, Conidiation and Stress Response in Penicillium expansum .

is a key gene for ergosterol biosynthesis in filamentous fungi, but its function in remains unknown. Our results showed that contains three genes, including , and . The expression levels of the three genes showed differences in the wild-type (WT) strain, and the expression level of was the highest, followed by . Deletion of , or in the WT strain revealed functional redundancy between them. Compared to the WT strain, , or knockout mutants reduced ergosterol levels, with deletion having the greatest effect. Furthermore, deletion of the three genes reduced sporulation of the strain, and Δ and Δ mutants showed defective spore morphology. In addition, Δ and Δ mutants were found to be more sensitive to cell wall integrity and oxidative stress. However, deletion of , or had no significant effect on colony diameter, spore germination rate, conidiophore structure of or pathogenicity to apple fruit. Taken together, , and have redundant functions and are all involved in ergosterol synthesis and sporulation in . In addition, and contribute to spore morphogenesis, cell wall integrity and response to oxidative stress in .