MOLECULAR MECHANISMS INVOLVED IN BACTERIAL SPECK DISEASE RESISTANCE OF TOMATO

An important recent advance in the field of plant-microbe interactions has been the cloning of genes that confer resistance to specific viru ses, bacteria, fungi or nematodes. Disease resistance (R) genes encode proteins with predicted structural motifs consistent with them having roles in signal recognition and transduction. The future challenge is to understand how R gene products specifically perceive defence-elici ting signals from the pathogen and transduce those signals to pathways that lead to the activation of plant defence responses. In tomatoes, the Pto kinase (product of the Pro R gene) confers resistance to strai ns of the bacterial speck pathogen, Pseudomonas syringae pv. tomato, t hat carry the corresponding avirulence gene avrPto. Resistance to bact erial speck disease is initiated by a mechanism involving the physical interaction of the Pto kinase and the AvrPto protein. This recognitio n event initiates signalling events that lead to defence responses inc luding an oxidative burst, the hypersensitive response and expression of pathogenesis-related genes. Pto-interacting (Pti) proteins have bee n identified that appear to act downstream of the Pto kinase and our c urrent studies are directed at elucidating the roles of these componen ts.