Fusarium wilts caused by different formae speciales of the soilborne phytopathogenic fungus Fusarium oxysporum provoke severe yield losses on many crop plants in Europe and world-wide. A better understanding of the molecular mechanisms controlling pathogenicity is needed in order to improve disease control strategies. Saponins are common plant secondary metabolites occurring in over 100 families including many major food crops. Many of them have pronounced antifungal properties, and it has been proposed that they act as pre-formed determinants of resistance to attack by fungi. Some pathogenic fungi have intrinsic resistance to the membranolytic action of saponins because of their membrane composition, whereas other produce enzymes (saponinases) that specifically detoxify particular plant saponins. These enzyme activities have been associated with the ability to attack certain plants.
The saponin alpha-tomatine, found in tomato plants, is toxic to a broad range of fungi. Fusarium oxysporum f.sp. lycopersici, a tomato pathogen, produces an extracellular enzyme, known as tomatinase, which catalyses the hydrolysis of alpha-tomatine into its nonfungitoxic forms, tomatidine and beta-lycotetraose. The aim of this project is to determine the significance of tomatinase in the pathogenicity of Fusarium oxysporum f.sp. lycopersici to tomato. The specific role of tomatinase in this plant-pathogen interaction will be first assessed by studying tomatinase-minus fungal mutants generated by targeted gene disruption and overproducing strains with constitutive expression of the tomatinase gene. Additionally, a reporter gene system will be used to analyse the mechanism by which tomatinase expression is regulated in vivo during the process of infection.