Rapid transcript accumulation of pathogenesis-related genes during an incompatible interaction in bacterial speck disease-resistant tomato plants

In the yeast two-hybrid system, the Pto kinase interacts with three putativ e transcription factors Pti4, Pti5 and Pti6. The Pti4/5/6 proteins contain a DNA binding domain that recognizes and binds a DNA sequence (5'-AGCCGCC-3 '; the `PR box') present in the promoter region of a large number of genes encoding `pathogenesis-related' (PR) proteins. We have now investigated the pathogen-induced expression of PR box-containing genes in tomato. We isola ted a tomato osmotin gene that contains two PR boxes in its promoter region and demonstrated that the abundance of the osmotin transcript rapidly incr eases during an incompatible interaction involving Pto-containing tomato pl ants and the bacterial pathogen Pseudomonas syringae pv. tomato expressing the avrPto gene. In addition, we found that transcripts of two other tomato PR genes (encoding endochitinase and beta-1,3-glucanase B) and at least on e ACC oxidase gene, all of which contain PR boxes in their promoter regions , rapidly accumulate in the incompatible interaction. These data support th e hypothesis that the tomato Pto kinase regulates the expression of certain defense genes in tomato by interaction with transcription factors that bin d the PR box.