Roles of pilT gene in pathogenicity of Xanthomonas oryzae pv.oryzicola on rice

Abstract:

[Objective] Our previous study found that a Tn5 transposon inserted mutant in pilT gene of Xanthomonas oryzae pv. oryzicola (Xoc) RS105 strain (the causal agent of bacterial leaf streak) significantly reduced bacterial virulence in susceptible rice plants, and the ability to trigger hypersensitive response (HR) on non-host tobacco. [Methods] To reveal the roles of pilT gene in bacterial pathogenicity in rice, we constructed a deletion mutant of pilT gene in Xoc RS105 named RΔpilT. Then we tested phenotypes of the mutant compared to the wild-type RS105 in bacterial virulence, motility and biofilm formation. [Results] The pilT mutant RΔpilT significantly reduced bacterial virulence in rice and the ability to trigger HR on tobacco. In addition, compared to RS105 strain, RΔpilT mutant displayed severely weakened motility on semisolid medium, and increased the production of biofilm. Full virulence, bacterial motility and biofilm formation was restored to the mutant when Xoc pilT was expressed in trans. Through qRT PCR analysis, we found that pilT gene was regulated by clp, rpfG, pilA and pilC. [Conclusion] These results indicate that pilT gene is essential for full bacterial virulence in rice possibly due to the association with the reduced motility and increased biofilm production by the pilT mutation, implying that the importance of further investigation on the function of PilT in composition of type IV pili in Xoc.