A SOIL-DWELLING Pseudomonas SP.593 HARBORING AN EXOGENOUS hrpZ GENE ELICITS A TYPICAL HYPERSENSITIVE RESPONSE IN TOBACCO AND SOYBEAN LEAVES

Pseudomonas sp.593 is a soil-dwelling bacterium unable to elicit any hypersensitive response (HR) in tobacco or soybean. The hrpZ gene, encoding an abundant Type III secretion system (T3SS) dependent protein, was cloned from a phytopathogen Pseudomonas syringae pv. syringae Van Hall CFCC 1336. The HrpZ harpin expressed in E. coli was purified to homogeneity, and used to raise polyclonal anti-HrpZ rabbit serum. The cloned hrpZ gene was then introduced into the soil bacterium Pseudomonas sp.593 via transformation of the plasmid pMEK-hrpZ. Western blotting and HR assay showed that the hrpZ-transformed Pseudomonas sp.593 was not only able to secret HrpZ harpin but also elicited a strong HR reaction in tobacco and soybean just as P. syringae did. In addition, bacterial cells were able to grow and multiply in the HR zone. Our results demonstrate that an avirulent strain can become a virulent-like pathogen, or a pathogen strain can broaden its host range once a single exogenous hrpZ gene cloned from a phytopathogen is introduced into a bacterium displaying phylogenetic diversity.