Botrytis cinerea laccase abolishes resveratrol toxicity and reduces Grape PR proteins solubility

Some grape proteins are structurally and functionally related to plant pathogenesis-related proteins. When challenging mature grape berries, Botrytis cinerea encounters these PR proteins as well the stilbenic phytoalexin trans-resveratrol and other grape polyphenols. To mimic these conditions, Botrytis cinerea was grown in vitro with proteins and polyphenols extracted from mature grapes and with trans-resveratrol. Results showed that in the presence of highly toxic amounts of trans-resverattol, grape polyphenols and proteins allowed total and partial recovery of fungal growth, respectively. These resveratrol-polyphenol or resveratrol-protein combinations also induced a strong release into the medium of laccase activity, which is likely to be involved in the trans-resveratrol detoxification process. Most grape proteins quickly disappeared from the culture when polyphenols and trans-resveratrol were supplied together and similar protein patterns were obtained in vitro by incubating grape proteins with grape polyphenols and/or trans-resveratrol with a purified B. cinerea laccase. Under these conditions, most protein became insoluble. The grape protein pattern obtained from grape berries infected by B. cinerea strongly resembled that obtained in vitro by incubating the grape proteins and polyphenols with the fungal laccase. It seems that B. cinerea, in the presence of the berry polyphenols and through laccase activity, easily neutralizes the toxicity of grape stilbenic phytoalexins and makes the grape pathogenesis-related proteins insoluble. Whether changes of grape proteins solubility affect the expression of proteinase genes and the proteolytic activity of B. cinerea is currently under investigation.