The Transcription Factor SsSR Mediates Ergosterol Biosynthesis and Virulence in Sclerotinia sclerotiorum

<i>Sclerotinia sclerotiorum</i>, known as a typical necrotrophic pathogenic fungus, exhibits a complex pathogenic mechanism. Research on <i>S. sclerotiorum</i> has primarily focused on oxalic acid, pathogenicity-related enzymes, and secreted proteins. In this study, we identified a transcription factor, SsSR (<i>S. sclerotiorum</i> Sterol-Related transcription factor), which regulates <i>S. sclerotiorum</i> infection by modulating virulence through ergosterol biosynthesis. We characterized the transcriptional activity of <i>SsSR</i> and its downstream target gene, <i>SsCYP51</i>. <i>SsSR</i> undergoes phosphorylation induced by the host plant, subsequently regulating the expression of <i>SsCYP51</i>. The deletion of <i>SsSR</i> or <i>SsCYP51</i> does not affect the growth or acid production of <i>S. sclerotiorum</i>, but it leads to a reduction in ergosterol, significantly diminishing virulence and impairing the stress tolerance of the hyphae. In summary, this study identifies a transcription factor, <i>SsSR</i>, that specifically regulates the virulence of <i>S. sclerotiorum</i>. <i>SsSR</i> upregulates the expression of <i>SsCYP51</i> through phosphorylation during the infection phase, leading to the synthesis of ergosterol, which enhances hyphal stress tolerance and thereby promotes infection.