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

erg4 is a key gene for ergosterol biosynthesis in filamentous fungi, but its function in Penicillium expansum remains unknown. Our results showed that P. expansum contains three erg4 genes, including erg4A , erg4B and erg4C . The expression levels of the three genes showed differences in the wild-type (WT) strain, and the expression level of erg4B was the highest, followed by erg4C . Deletion of erg4A , erg4B or erg4C in the WT strain revealed functional redundancy between them. Compared to the WT strain, erg4A , erg4B or erg4C knockout mutants reduced ergosterol levels, with erg4B deletion having the greatest effect. Furthermore, deletion of the three genes reduced sporulation of the strain, and Δ erg4B and Δ erg4C mutants showed defective spore morphology. In addition, Δ erg4B and Δ erg4C mutants were found to be more sensitive to cell wall integrity and oxidative stress. However, deletion of erg4A , erg4B or erg4C had no significant effect on colony diameter, spore germination rate, conidiophore structure of P. expansum or pathogenicity to apple fruit. Taken together, erg4A , erg4B and erg4C have redundant functions and are all involved in ergosterol synthesis and sporulation in P. expansum . In addition, erg4B and erg4C contribute to spore morphogenesis, cell wall integrity and response to oxidative stress in P. expansum .