Tomatidine and lycotetraose, hydrolysis products of α-tomatine by Fusarium oxysporum tomatinase, suppress induced defense responses in tomato cells

Abstract

Many fungal pathogens of tomato produce extracellular enzymes, collectively known as tomatinases, that detoxify the preformed antifungal steroidal glycoalkaloid α-tomatine. Tomatinase from the vascular wilt pathogen of tomato Fusarium oxysporum f. sp. lycopersici cleaves α-tomatine into the aglycon tomatidine (Td) and the tetrasaccharide lycotetraose (Lt). Although modes of action of α-tomatine have been extensively studied, those of Td and Lt are poorly understood. Here, we show that both Td and Lt inhibit the oxidative burst and hypersensitive cell death in suspension-cultured tomato cells. A tomatinase-negative F. oxysporum strain inherently non-pathogenic on tomato was able to infect tomato cuttings when either Td or Lt was present. These results suggest that tomatinase from F. oxysporum is required not only for detoxification of α-tomatine but also for suppression of induced defense responses of host.