TOMATINASE INDUCTION IN FORMAE SPECIALES OF FUSARIUM-OXYSPORUM NONPATHOGENIC OF TOMATO PLANTS

The antifungal compound alpha-tomatine has been reported to provide a preformed chemical barrier in tomato plants against phytopathogenic fu ngi. Fusarium oxysporum f.sp. lycopersici and other tomato pathogens p roduce extracellular enzymes induced by alpha-tomatine. These enzymes, known as tomatinases, provoke deglycosylation of alpha-tomatine yield ing less toxic derivatives. To date, tomatinase activities have been a ssociated exclusively with fungi which are able to infect tomato plant s. Here, we have established that another tomato pathogen, F. oxysporu m f.sp. radicis-lycopersici, also produces an inducible alpha-tomatine detoxifying enzyme. In addition, we found that other formae speciales which are not pathogens of tomato such as tuberosi, melonis, niveum a nd gladioli also have inducible tomatinases. These formae speciales ar e natural pathogens of other hosts, some of which are phylogenetically related to tomato but others are not. The tomatinases found in these formae speciales have the same molecular mass and act mechanistically in the same way as the tomatinase from F. oxysporum f.sp, lycopersici, i.e. catalysing the hydrolysis of alpha-tomatine into the less fungit oxic molecules, tomatidine and beta-lycotetraose. These enzymes were r ecognized by polyclonal antibodies raised against tomatinase from F. o xysporum f.sp. lycopersici. These observations suggest that tomatinase enzymes are analogous in the different formae speciales studied. The possible role of tomatinases in fungi which are not tomato pathogens a nd the phylogenetic relationship between the different formae speciale s of F. oxysporum are discussed. (C) 1997 Academic Press Limited.