Detoxification of α-tomatine by Botrytis cinerea

Thirteen Botrytis cinerea isolates from several host plants were tested for their ability to degrade the saponin alpha-tomatine; all but one strain could deglycosylate alpha-tomatine. The exception, strain M3, (collected from grape vine) was more sensitive to alpha-tomatine and was not aggressive on tomato, suggesting a role for alpha-tomatine degradation in the interaction between B. cinerea and tomato. The mechanism of degradation was studied by thin layer-chromatography, Matrix assisted laser desorption/ionization time-of-flight mass spectroscopy and gas chromatography and, in contrast to published data, beta(1)-tomatine was identified as the end-product, i.e. the B. cinerea tomatinase must represent a beta-xylosidase. The tomatinase activity was induced by alpha-tomatine but not by other steroidal glycoalkaloid saponins such as chaconine or solanine, and is not subject to carbon or nitrogen catabolite repression. The corresponding enzyme was purified and found to have a molecular weight of 70 kDa, a pH-optimum of 6.0, and a pI of 5.1. (C) 1998 Academic Press.