Critical Role of Transcription Factor CtSR in Mediating Ergosterol Biosynthesis and DMI Fungicides Sensitivity in <i>Colletotrichum truncatum</i>

Anthracnose caused by <i>Colletotrichum truncatum</i> severely impacts global fruit/vegetable yields. Unlike other <i>Colletotrichum</i> species, <i>C. truncatum</i> exhibits inherent resistance to some sterol demethylation inhibitors (DMIs), necessitating an understanding of ergosterol synthesis regulation and resistance mechanisms. A transcription factor, CtSR (CTRU02_06681), that regulates the DMI sensitivity in <i>C. truncatum</i> was identified in our study. Deletion of <i>CtSR</i> rendered a naturally resistant isolate highly sensitive to DMIs, significantly reduced total ergosterol levels, decreased <i>CYP51s</i> expression compared to the wild type, and abolished DMI-induced expression of <i>CYP51s</i>. Deletion of <i>CtSR</i> reduced mycelial growth and virulence and made the strain highly sensitive to oxidative stress but did not affect its sensitivity to osmotic stress. Transcriptomic analysis and yeast one-hybrid assays confirmed that CtSR directly binds the conserved promoter motif CGAATACGAA to regulate ergosterol biosynthesis genes. Taken together, our study demonstrates a critical role for CtSR in the regulation of ergosterol biosynthesis and DMI interactions in <i>C. truncatum</i>, which may have significant practical implications.