Functional analysis of the Pseudomonas syringae rulAB determinant in tolerance to ultraviolet B (290-320 nm) radiation and distribution of rulAB among P-syringae pathovars

The effect of the plasmid-encoded ruIAB (resistance to ultraviolet radiatio n) determinant on responses of Pseudomonas syringae to ultraviolet-B (UV-B) radiation and the distribution of ruIAB among pathovars of P. syringae wer e determined. The cloned ruIAB determinant and the native ruIAB+ plasmid pP SR1 both conferred approximately a 10-fold increase in survival on P. syrin gae pv. syringae FF5 following increasing doses of UV-B radiation. ruIAB+ P .syringae strains also maintained significantly larger epiphytic population s on leaf surfaces irradiated with UV-B. ruIAB-insertional mutants, constru cted in two native ruIAB+ strains, were from 10- to 100-fold more sensitive to UV-B radiation. The UV tolerance phenotype and the ruIAB genes were wid ely distributed among P. syringae pathovars isolated from varied plant host s throughout the world and within a broad range of genotypic backgrounds of P. syringae pv. syringae. With one exception, the ruIAB determinant was ha rboured on pPT23A-like plasmids; these replicons are indigenous residents o f the species P. syringae and also tend to encode determinants of importanc e in host-pathogen interactions.