Functional Analysis of the C-5 Sterol Desaturase PcErg3 in the Sterol Auxotrophic Oomycete Pathogen Phytophthora capsici

Although sterols play an important role in most eukaryotes, some oomycetes, including spp., have lost the sterol synthesis pathway. Nevertheless, the gene encoding C-5 sterol desaturase in the sterol synthesis pathway is still present in the genomes of spp. , a destructive pathogen with a broad range of plant hosts, poses a significant threat to the production of agriculture. This study focused on the gene in ( ) and explored its function in this pathogen. It showed that the gene could be expressed in all tested developmental stages of , with sporangium and mycelium displaying higher expression levels. A potential substrate of Erg3 (stellasterol) was used to treat the wild-type strain and a Δ transformant, and their sterol profiles were determined by GC-MS. The wild-type strain could convert stellasterol into the down-stream product while the transformant could not, indicating that PcErg3 retains the C-5 sterol desaturase activity. By comparing the biological characteristics of different strains, it was found that is not important for the development of . The pathogenicity of the Δ transformants and the wild-type strain was comparable, suggesting that is not necessary for the interaction between and its hosts. Further investigations revealed that the Δ transformants and the wild-type strain displayed a similar level of tolerance to external adversities such as unsuitable temperatures, high osmotic pressures, and intemperate pH, signifying that is not essential for to cope with these environmental stresses.