Exoglucanase Genes (WaEXG1 and WaEXG2) In Wickerhamomyces anomalus Respond to the Nutritional Environment and Differentially to Postharvest Pathogens

Introduction Wickerhamomyces anomalus, a yeast that can be used as a postharvest biocontrol agent is known to produce killer toxins that have been demonstrated to be exoglucanases, coded by the genes WaEXG1 and WaEXG2 (Mucilli et al., 2013). Among a variety of mechanisms, glucanase production by antagonistic yeast have been reported to play a role in inhibiting other fungi. The aim of the present study was to examine the expression of these genes using RT-qPCR. Materials and Methods WaEXG1 and WaEXG2 gene expression in W. anomalus was determined when the yeast was grown in wounds made in oranges either non-inoculated or inoculated with spores of Penicillium digitatum, or in minimal salt (MS) media supplemented with cell walls of P. digitatum or Botrytis cinerea, and presented as fold-change relative to the expression of the genes at T0 in NYDB (nutrient broth, yeast extract, glucose). Expression was quantified by RT-qPCR utilizing gene-specific primers over 48h of incubation. Results Expression of WaEXG1 increased over a 48 h period when the yeast was grown in NYDB, non-inoculated and inoculated wounds, while it was stable over 48 h when the yeast was grown on MS media supplemented with cell walls of P. digitatum or B. cinerea. In contrast, the expression of WaEXG2 was stable over a 48 h period of incubation when the yeast was grown in NYDB, non-inoculated or inoculated wounds, but it increased dramatically over the same period when the yeast was grown in MS media with P. digitatum cell walls, with the highest level of induction observed at 24 and 48 h. A much smaller induction of WaEXG2 expression occurred in MS media supplemented with B. cinerea cell walls, although the yeast population decreased dramatically in MS media containing cell walls of either pathogen. Discussion These results suggest that while WaEXG2 responds to the nutritional environment, it may also be responsive to the presence of a specific pathogen (P. digitatum).