Potential role of exoglucanase genes (WaEXG1 and WaEXG2) in the biocontrol activity of Wickerhamomyces anomalus

The use of yeasts, including Wickerhamomyces anomalus, as biocontrol agents of fungi responsible for postharvestdiseases of fruits and vegetables has been investigated for the past two decades. Among a variety of mechanisms, the production of glucanases coded by the Bkiller genes^WaEXG1 and WaEXG2 have been reported to play a role inthe ability of yeast to inhibit other fungi. The objective of thepresent study was to determine the expression of these genesby RT-qPCR, utilizing gene-specific primers, whenW. anomalus was grown on grape berries and oranges that were either non-inoculated or inoculated with Botrytis cinereaor Penicillium digitatum, or in minimal media supplementedwith cell walls of various plant pathogens and differentamounts of glucose. Results indicated that WaEXG2 was more responsive than WaEXG1 to the nutritional environment (includingthe addition of glucose to cell wall-amended media)in vitro and appeared to play a greater role in the cellular metabolism of W. anomalus. WaEXG2 expression also appeared to be more responsive to the presence of cell walls of P. digitatum and B. cinerea than other fungal species, whereasthe same level of induction was not seen in vivo when the yeast was grown in wounded/pathogen-inoculated fruits.