Role of Flagella and Flagellin in Plant — Pseudomonas syringae Interactions

Abstract

The role of flagella and monomer flagellin of Pseudomonas syringae pv. tabaci in plant-bacteria interactions was investigated by using non-polar fliC or fliD mutants. These mutants deleted the open reading frames for fliC and fliD, respectively, and both mutants lost all flagella and motility. The ΔfliC mutant did not produce flagellin, whereas ΔfliD mutant, that lost HAP2 protein, secreted a large amount of monomer flagellin in the culture medium. Inoculation of tomato leaves with wild type and ΔfliD mutant of P. s. pv. tabaci induced HR, whereas the ΔfliC mutant caused symptom-like change and propagated as P. s. pv. tomato. In tomato suspension cultured cells, wild type P. s. pv. tabaci induced visible HR-like changes. The ΔfliC mutant did not induce the HR, but the response was activated by the ΔfliD mutant. The expression of typical defence genes such as PAL and hsr203J was rapidly and strongly induced by inoculation with the ΔfliD mutant compared to inoculation with wild type P. s. pv. tabaci. On the other hand, both fliC and fliD mutants were reduced in virulence when inoculated into host tobacco leaves. Furthermore, complementation of fliC gene in ΔfliC mutant restored motility and HR-inducing ability in tomato, and virulence in tobacco. These results suggest that the monomer flagellin of P. s. pv. tabaci is an essential factor in the elicitation of HR in non host tomato cells, and flagella are required for complete virulence in host tobacco cells.