THE PTO KINASE CONFERRING RESISTANCE TO TOMATO BACTERIAL SPECK DISEASE INTERACTS WITH PROTEINS THAT BIND A CIS-ELEMENT OF PATHOGENESIS-RELATED GENES

In tomato, the Pto kinase confers resistance to bacterial speck diseas e by recognizing the expression of a corresponding avirulence gene, av rPto, in the pathogen Pseudomonas syringae pv, tomato, Using the yeast two-hybrid system, we have identified three genes, Pti4, Pti5 and Pti 6, that encode proteins that physically interact with the Pto kinase, Pti4/5/6 each encode a protein with characteristics that are typical o f transcription factors and are similar to the tobacco ethylene-respon sive element-binding proteins (EREBPs). Using a gel mobility-shift ass ay, we demonstrate that, similarly to EREBPs, Pti4/5/6 specifically re cognize and bind to a DNA sequence that is present in the promoter reg ion of a large number of genes encoding 'pathogenesis-related' (PR) pr oteins. Expression of several PR genes and a tobacco EREBP gene is spe cifically enhanced upon Pto-avrPto recognition in tobacco. These obser vations establish a direct connection between a disease resistance gen e and the specific activation of plant defense genes.