Abstract
Ergosterol (ERG) is a potential target for the development of antifungal agents against Penicillium digitatum, the pathogen of green mold in citrus fruits. This study examined the mechanism by which citronellal, a typical terpenoid of Cymbopogon nardus essential oil, acts on ergosterol to exhibit its antifungal activity against P. digitatum. We previously reported that citronellal inhibited the growth of P. digitatum with 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 of P. digitatum by down-regulating the ERG genes responsible for conversion of lanosterol to ergosterol, the key downregulated gene being ERG3, due to the observed accumulation of ergosta-7,22-dienol.
Highlights
Green mold, caused by the pathogen Penicillium digitatum, is the major postharvest disease of citrus during harvesting and postharvest handling processes [1]
It is key to the structural integrity of the cell membranes and, as such, the main target of the majority of the available antifungals [32,33], which interfere with its function either through inhibition of various steps in ergosterol biosynthesis or by complexing directly with membrane ergosterol [24]
Our results show that treatment of P. digitatum with citronellal led to a significant inhibition of ergosterol biosynthesis and damage to the cell membrane
Summary
Green mold, caused by the pathogen Penicillium digitatum, is the major postharvest disease of citrus during harvesting and postharvest handling processes [1]. Citronellal was reported to be effective in inhibiting the growth of three pathogenic Penicillium strains including P. digitatum, P. italicum, and P. ulaiense, with the inhibition zone ranging from 31 to 43 mm2 [12]. A number of studies have shown that essential oils such as citral, eugenol, thymol, carvacrol, and perillaldehyde can significantly reduce the ergosterol content in the cell membranes of P. digitatum, Aspergillus species, and Candida species, causing abnormal cell membrane function [20,21,22,23,24,25,26]. This study was designed (i) to evaluate the effect of citronellal on the plasma membrane integrity of P. digitatum, (ii) to determine its effect on lanosterol and ergosterol contents and on sterol composition, and (iii) to analyze its effect on gene expression levels in ergosterol biosynthesis of P. digitatum
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
