Objective Role of xatB gene cluster played in regulating the infection of Xanthomonas oryzae pv. oryzacola (Xoc) on rice plants was investigated.

Method Single, double, and triple mutants of Xoc on xatB, Xoc_1597 (mfd), and Xoc_1599 (rlmJ) in the cluster as well as the corresponding complemented strains were constructed. Pathogenicity of the mutated and complemented wild-type strains were detected by a punching method, and growth, extracellular enzyme activities, and motility determined by plate culture.

Result All xatB, mfd, and rlmJ mutations resulted in a significant decline in the virulence of Xoc. However, the rlmJ mutation inhibited, while mfd promoted, the growth, motility, and extracellular polysaccharide (EPS) synthesis; but the mfd complementation retarded those functions of the pathogen. The double and triple mutants differed from the single mutants in phenotypes as well as antagonistic or synergistic effects on Xoc.

Conclusion XatB, Mfd, and RlmJ significantly affected the Xoc virulence on rice plants. The complex relationship requires further investigation.