[Function of a two-component system RpfCxoc/RpfGxoc in Xanthomonas oryzae pv. oryzicola]

To elucidate the biological functions of a two-component system RpfCxoc/RpfGxoc in Xanthomonas oryzae pv. oryzicola (Xoc).

Based on the genome template from Xoc wild-type strain Rs105, the rpfCxoc and rpfGxoc genes were amplified by polymerase chain reaction (PCR). The in-frame deletion mutations of rpfCxoc, rpfGxoc and rpfGCxoc (rpfCxoc and rpfGxoc double genes) were performed by the suicide vector pK18mobsacB, and determined diffusible signal factor (DSF) biosynthesis, pathogenicity in host rice, biofilm, extracellular polysaccharide (EPS) production and cell morphology.

rpfCxoc and rpfGxoc were cloned from the genomic DNA of Rs105. PCR analysis demonstrated that the rpfCxoc, rpfGxoc and rpfGCxoc genes were in-frame deleted successfully. Compared to the wild-type strain Rs105, DSF were overproduced in deltarpfCxoc and deltarpfGCxoc, but DSF production was remarkably decreased in deltarpfGxoc. The DSF production of these mutants was restored by introducing the complemented cosmid pUFR-rpfCxoc, pUFR-rpfGxoc and pUFR-rpfGCxoc, respectively. Subsequent experimental results indicated that mutation of rpfCxoc, rpfGxoc and rpfGCxoc resulted in pathogenicity loss of Xoc in host rice, and decreased biosynthesis level of EPS at 34.1%-48.5% compared to that of Rs105. In L medium (Tryptoen, 10 g/L; yeast extract, 5 g/L; sodium chloride, 5 g/L; D-glucose, 1 g/L; pH7.0) , Rs105 was growing at planktonic pattern, but the mutation of rpfCxoc and rpfGxoc led to Xoc cell aggregation at the wall of the flaks at the air-liquid interfaces, and deltarpfGxoc generated reticulation biofilm at the bottom of the flaks. But deltarpfGCxoc only generated reticulation biofilm at the bottom of the flaks.

The two-component system RpfCxoc/RpfGxoc modulated DSF biosynthesis, EPS production and biofilm dispersal of Xoc, which was required for the pathogenicity of Xoc in host rice.