Oral: Bacterial Virulence Regulation
Characterization of RpfB-dependent DSF-Family Quorum Sensing Signal Turnover System in the Phytopathogen Xanthomonas
L. ZHOU (1), X. Wang (1), Y. He (1) (1) Shanghai Jiao Tong University, China
Molecules of the diffusible signal factor (DSF)-family are a class of quorum sensing (QS) signals used by the phytopathogens Xanthomonas. RpfB has recently been reported as a fatty acyl-CoA ligase (FCL) that activates a wide range of fatty acids to their CoA esters in vitro. Through genetic and biochemistry analysis, we found that RpfB represents a naturally occurring DSF-family signal turnover system in X. campestris pv. campestris (Xcc) and X. oryzae pv. oryzae (Xoo). RpfB effectively turns over DSF-family signals DSF and BDSF in vivo. RpfB FCL enzymatic activity is required for DSF and BDSF turnover in Xcc and Xoo. The expression of rpfB is growth phase-dependent and its expression is significantly enhanced when Xanthomonas cells enter the stationary phase. DSF regulates rpfB expression in a concentration-dependent manner. rpfB expression is also negatively regulated by the DSF signaling components RpfC, RpfG, and Clp. Although most of our findings have suggested that the DSF-family signal turnover systems are generally consistent in Xcc and Xoo, we also identified some discrepancies in bacterial pathogenesis and virulence factor production between the rpfB mutants of Xcc and Xoo. Therefore, our findings strongly indicated the complexity of the RpfB-dependent DSF-family signal turnover system, which is likely fine-tuned to facilitate infection process in different hosts (rice versus crucifers).