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, which causes rice bacterial leaf blight, to bismerthiazol has been detected in China since the 1990s. The strains resistant to bismerthiazol on rice plants were more sensitive to bismerthiazol than wild-type (WT) strains in vitro. Here, quantitative PCR was applied to detect the fold expression of adenosine triphosphate-dependent proteases, ClpP and its subunits, which withstand stresses including bactericides in bismerthiazol-resistant strains and their parental susceptible WT strain (ZJ173). Results showed that the expression of ClpP and its subunits was higher in bismerthiazol-resistant strains than in ZJ173. They were upregulated during the early growth phase and downregulated during the middle growth phase in ZJ173 treated with bismerthiazol but did not change in the resistant strains. ClpP and its subunits were overexpressed in X. oryzae pv. oryzae in this study; the higher expression of these genes increased sensitivity in vitro and increased resistance in vivo to bismerthiazol. Bismerthiazol inhibition of exopolysaccharide (EPS) production, biofilm production, and motility was also lower in ClpP and its subunits' overexpression mutants of X. oryzae pv. oryzae. The deletion mutants of ClpP and its subunits in ZJ173 decreased pathogenicity, biofilm production, swimming ability, EPS 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 X. oryzae pv. oryzae. Taken together, our results indicated that ClpP and its subunits of X. oryzae pv. oryzae influenced resistance to bismerthiazol.