MOLECULAR-BASIS OF GENE-FOR-GENE SPECIFICITY IN BACTERIAL SPECK DISEASE OF TOMATO

Transient expression of the Pseudomonas syringae avirulence gene avrPt o in plant cells resulted in a Pto-dependent necrosis. The AvrPto avir ulence protein was observed to interact directly with the Pto resistan ce protein in the yeast two-hybrid system. Mutations in the Pto and av rPto genes which reduce in vivo activity had parallel effects on assoc iation in the two-hybrid assay. These data suggest that during infecti on the pathogen delivers AvrPto into the plant host cell and that resi stance is specified by direct interaction of Pto with AvrPto.