Insights into the roles of two genes of the histidine biosynthesis operon in pathogenicity of Xanthomonas oryzae pv. oryzicola

Xanthomonas oryzae pv. oryzicola (Xoc) is a X. oryzae pathovar that causes bacterial leaf streak in rice. In this study, we performed functional characterization of a nine-gene his operon in Xoc. Sequence analysis indicates that this operon is highly conserved in Xanthomonas spp. Auxotrophic assays confirmed that the his operon was involved in histidine biosynthesis. We found that two genes within this operon -trpR and hisB- were required for virulence and bacterial growth in planta. Further research revealed that trpR and hisB play different roles in Xoc. The trpR acts as a transcriptional repressor and could negatively regulate the expression of hisG, -D, -C, -B, -H, -A, and -F. hisB, which encodes a bifunctional enzyme implicated in histidine biosynthesis, was shown to be required for xanthomonadin production in Xoc. The disruption of hisB reduced the transcriptional expression of five known shikimate pathway-related genes xanB2, aroE, aroA, aroC, and aroK. We found that the his operon in Xoc is not in...