XanFur, a novel Fur protein induced by H₂O₂, positively regulated by the global transcriptional regulator Clp and required for the full virulence of Xanthomonas oryzae pv. oryzae in rice

Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive diseases in rice. However, the pathogenic mechanisms of Xoo have not been fully understood. In this study, we identified a novel ferric uptake regulator (Fur) protein, XanFur, in Xoo, which is conserved among the major pathogens of Xanthomonas species, but has no obvious sequence identity with reported Fur proteins. Gene deletion indicated that xanfur is required for the full virulence of Xoo in rice. The expression of xanfur was significantly induced by 0.1 mM H(2)O(2 )and its deletion caused a significant decrease in the tolerance of Xoo to H2O2, suggesting that xanfur is likely involved in the resistance of Xoo to the oxidative stress caused by H(2)O(2 )in rice. The loss of xanfur also caused significant reduction in extracellular polysaccharide production, biofilm formation, and cell motility, suggesting that xanfur may be also involved in regulating these virulence determinants of Xoo. Furthermore, both in vivo and in vitro experimental results demonstrated that the global transcriptional regulator Clp positively regulated the expression of xanfur by directly binding to its promoter region, especially in the presence of 0.1 mM H2O2, presenting the cellular regulatory pathway for the expression of this gene. These results not only contribute to a better understanding of the interaction mechanisms between rice and Xoo, but also provide reference to developing high-effective bactericides by targeting to the Fur protein in Xoo to control bacterial leaf blight in rice.