ATP-dependent protease ClpP and its subunits ClpA, ClpB, and ClpX involved in the field bismerthiazol-resistance in Xanthomonas oryzae pv. oryzae

Resistance of Xanthomonas oryzae pv. oryzae (Xoo), which causes rice bacterial leaf blight, to bismerthiazol has been detected in China since the 1990s. Interestingly, the strains resistant to bismerthiazol on rice plants were more sensitive to bismerthiazol than wild-type (WT) strains in vitro. Here, qPCR was applied to detect the fold expression of ATP-dependent proteases, ClpP and its subunits, which cope with stresses including bactericides in bismerthiazol-resistant strains and their parental susceptible WT strain (ZJ173). Results showed that the expression of ClpP and its subunits were all higher in bismerthiazol-resistant strains than that in ZJ173. They were up-regulated during early growth phase and down-regulated during middle growth phase in ZJ173 treated with bismerthiazol but did not change in the resistant strains. ClpP and its subunits were overexpressed in Xoo in this study, the higher expression of these genes increased sensitivity in vitro and enhanced resistance in vivo to bismerthiazol. Inhibition of bismerthiazol to exopolysaccharide production, biofilm, and motility was also reduced in ClpP and its subunit's overexpression mutants of Xoo. The deletion mutants of ClpP and its subunits in ZJ173 abated pathogenicity, biofilm production, swimming ability, exopolysaccharide production, and growth in low-nutrient environments. Moreover, ClpP and its subunits may act downstream of the histidine utilization pathway, which could be inhibited by bismerthiazol in Xoo. Taken together, our results indicated that ClpP and its subunits of Xoo influenced the resistance to bismerthiazol.