Knot formation caused by Pseudomonas syringae subsp savastanoi on olive plants is hrp-dependent

Sisto, A., Cipriani. M. G., and Morea, M. 2004. Knot formation Caused by P,Pseudomonas syringae subsp. savastanoi on olive plants is hrp-dependent. Phytopathology 94:484-489. The virulence of Pseudomonas syringae subsp. savastanoi. which causes hyperplastic symptoms (knots) on olive plants. is associated with secreted phytohormones. We identified a Tn5-induced mutant Of P syringae suhsp. savastanoi that did not cause disease symptoms oil olive plants although it was still able to produce phytormones. In addition, the Mutant failed to elicit a hypersensitive response in a nonhost plant. Molecular characterization of the Mutant revealed that a single Tn5 insertion occurred within an open reading frame encoding a protein 92% identical to the HrcC protein of P syringae pv. syringae. Moreover, sequence analysis revealed that the gene encodim, the HrcC protein in P syringae subsp. savastanoi was part of an operon that included five lenes arranged its in other phytopathogenic bacteria. These results imply that hrp/hrc genes are functional in P. syringae subsp. savastanoi and that they play a key role in the pathogenicity of this plant pathogen.