<i>Phytophthora capsici</i> sterol reductase PcDHCR7 has a role in mycelium development and pathogenicity

Abstract

The <i>de novo</i> biosynthesis of sterols is critical for the majority of eukaryotes; however, some organisms lack this pathway, including most oomycetes. <i>Phytophthora</i> spp. are sterol auxotrophic but, remarkably, have retained a few genes encoding enzymes in the sterol biosynthesis pathway. Here, we show that <i>PcDHCR7,</i> a gene in <i>Phytophthora capsici</i> predicted to encode Δ7-sterol reductase, displays multiple functions. When expressed in <i>Saccharomyces cerevisiae</i>, PcDHCR7 showed the Δ7-sterol reductase activity. Knocking out <i>PcDHCR7</i> in <i>P. capsici</i> resulted in loss of the capacity to transform ergosterol into brassicasterol, which means PcDHCR7 has the Δ7-sterol reductase activity in <i>P. capsici</i> itself<i>.</i> This enables <i>P. capsici</i> to transform sterols recruited from the environment for better use. The biological characteristics of <i>ΔPcDHCR7</i> transformants were compared with those of the wild-type strain and a <i>PcDHCR7</i> complemented transformant, and the results showed that <i>PcDHCR7</i> plays a key role in mycelium development and pathogenicity of zoospores. Further analysis of the transcriptome indicated that the expression of many genes changed in the <i>ΔPcDHCR7</i> transformant, which involve in different biological processes. It is possible that <i>P. capsici</i> compensates for the defects caused by the loss of <i>PcDHCR7</i> by remodelling its transcriptome.