Xanthomonas oryzae pv. oryzae requires H-NS-family protein XrvC to regulate virulence during rice infection

Histone-like nucleoid-structuring (H-NS) proteins, which are conserved in Gram-negative bacteria, bind DNA and act as the global transcriptional repressors. In this study, we identified and characterized the xrvC gene encoding a H-NS protein in Xathomonas oryzae pv. oryzae (Xoo) Philippines strain PXO99(A). Compared with the wild type, the xrvC-deficient mutant of PXO99(A) (named PXO99 Delta xrvC) showed a reduced growth rate in both nutrient-rich and nutrient-limited media. Interestingly, PXO99 Delta xrvC exhibited significantly reduced virulence on rice cultivar IRBB214, but its virulence on 31 other rice cultivars was not affected. Transcriptional analysis revealed that the expression of hrpG, hrpX and hpa1 and of 15 out of 18 tested non-TAL (transcription activator-like) effector genes was decreased significantly in the xrvC mutant compared with that in the wild type. In addition, loss of xrvC also impaired the induction of the rice susceptibility gene Os8N3 in IRBB214 by PXO99(A). Our results suggest that the xrvC gene is involved in bacterial growth, and it plays a vital role in virulence by positively regulating the expression of hrp genes and non-TAL effector genes in PXO99A and the susceptibility gene Os8N3 in rice.