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 disease by recognizing the expression of a corresponding avirulence gene, avrPto, in the pathogen Pseudomonas syringae pv. tomato. Using the yeast two-hybrid system, we have identified three genes, Pti4, Pti5 and Pti6, that encode proteins that physically interact with the Pto kinase. Pti4/5/6 each encode a protein with characteristics that are typical of transcription factors and are similar to the tobacco ethylene-responsive element-binding proteins (EREBPs). Using a gel mobility-shift assay, we demonstrate that, similarly to EREBPs, Pti4/5/6 specifically recognize and bind to a DNA sequence that is present in the promoter region of a large number of genes encoding 'pathogenesis-related' (PR) proteins. Expression of several PR genes and a tobacco EREBP gene is specifically enhanced upon Pto-avrPto recognition in tobacco. These observations establish a direct connection between a disease resistance gene and the specific activation of plant defense genes.