Agrobacterium rhizogenes rolA gene promotes tolerance to Fusarium oxysporum f. sp. lycopersici in transgenic tomato plants (Solanum lycopersicum L.).

In order to assess the role of Agrobacterium rhizogenes rol genes on the defence response of plants to pathogens, tomato plants (Solanum lycopersicum L.) were transformed with the rolA gene. Consistently with previous descriptions of rolA-induced phenotype, insertion of this gene had a pleiotropic effect determining highly aberrant plants, with wrinkled, intensely green leaves, thick stems and small fruits often lacking seeds. Infection of transgenic plants with the phytopathogenic fungus Fusarium oxysporum f. sp. lycopersici showed the acquirement of resistance/tolerance to the pathogen as evaluated both on the primary transformants by electrolyte leakage and on the transgenic progenies by direct infection. Determination of the endogenous levels of indole-3-acetic acid (IAA) and abscisic acid (ABA) showed a 30-35 % decrease of both phytohormones in rolA plants harbouring three copies of the transgene compared to the controls, while a significantly lower level of ABA was observed in plants with one copy of the transgene. This is the first demonstration of the direct involvement of rolA gene in plant pathogen tolerance acquisition.