Citronellal Exerts Its Antifungal Activity by Targeting Ergosterol Biosynthesis in Penicillium digitatum

Ergosterol (ERG) is a potential target for the development of antifungal agents againstPenicillium digitatum, the pathogen of green mold in citrus fruits. This study examined the mechanism by which citronellal, a typical terpenoid ofCymbopogon nardusessential oil, acts on ergosterol to exhibit its antifungal activity againstP. digitatum. We previously reported that citronellal inhibited the growth ofP. digitatumwith minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 1.36 and 2.72 mg/mL, respectively. In citronellal-treated cells, the membrane integrity and ergosterol contents significantly decreased, whereas lanosterol, which serves as a precursor for ergosterol biosynthesis, massively accumulated. Addition of 150 mg/L of exogenous ergosterol decreased the inhibitory rate of citronellal, restoring the ergosterol content and hence the membrane structure to normal levels, and triggered expression of nearly all ERG genes. Based on our findings, we deduce that citronellal damages the cell membrane integrity ofP. digitatumby down-regulating the ERG genes responsible for conversion of lanosterol to ergosterol, the key downregulated gene beingERG3, due to the observed accumulation of ergosta-7,22-dienol.Keywords:citrus;pathogen;ergosterol;ERG genes;cell membrane integrity