EXOGLUCANASE GENES (WaEXG1 and WaEXG2) ARE INDUCED IN WICKERHAMOMYCES ANOMALUS WHEN THE YEAST IS GROWN ON GRAPE BERRIES AND GRAPE BERRIES INOCULATED WITH BOTRYTIS CINEREA

The use of yeasts, including Wickerhamomyces anomalus, as biocontrol agents against fungi responsible for postharvest diseases of fruits and vegetables has been investigated for the past two decades. Among a variety of mechanisms, the production and secretion of glucanases have been reported to play a role in the ability of yeast to inhibit other fungi. Some yeasts also produce different types of “killer toxins” that presumably provide a competitive advantage against other microbes. Two killer toxins produced by W. anomalus have been previously demonstrated to be exoglucanases that are coded by the genes, WaEXG1 and WaEXG2. The objective of the present study was to determine the expression of these genes when W. anomalus was grown on halved grape berries that were either non-inoculated or inoculated with spores of Botrytis cinerea, or in minimal media supplemented with cell walls of the pathogen. Expression profiles over a 48 h period of incubation were analyzed by RT-qPCR utilizing gene-specific primers and compared to glucanase gene expression in the NYDB (control). Results indicated that expression of WaEXG1 at 48 h was 3.5, 3 and 4 fold greater than the control at T0, in the control, non-inoculated grape berries, and inoculated grape berries, respectively. Expression of WaEXG1in a minimal medium supplemented with cell walls of Botrytis, was also induced after 48 h, but at a much lower level than in the other treatments. An increase in the expression of WaEXG2 over a 48 h period was also observed, with the highest levels observed in the controls and the lowest in the minimal medium containing Botrytis cell walls. These results suggest that while both glucanase genes respond to the nutritional environment, WaEXG1 may be more responsive to the presence of a specific pathogen.