植物病原黄单胞菌退出群体感应生理状态的分子机制和生物学意义

Molecular mechanisms and biological significance of the naturally occurring turnover of DSF-family quorum sensing signal in the phytopathogen Xanthomonas

摘要:

黄单胞菌是一类引起多种作物病害的病原细菌总称。它们利用自身产生的DSF（Diffusible signaling factor）-家族群体感应（quorum sensing，QS）信号分子感应群体密度，调控致病相关基因的表达。当黄单胞菌培养达到对数生长后期时，培养体系中DSF信号分子浓度迅速降低，呈现一种典型的群体感应信号反转（turnover）现象。编码脂酰辅酶A连接酶的基因rpfB在黄单胞菌生长后期表达量显著提高，敲除rpfB导致DSF生物合成显著提高，因此，RpfB参与DSF-家族QS信号分子的降解，在群体感应后期引导黄单胞菌退出群体感应状态。DSF信号通过RpfC/RpfG双组分系统、环二鸟苷酸和全局性转录因子Clp负调控rpfB的表达。DSF群体感应信号关键降解基因rpfB存在于多种细菌中，表明该信号反转机制相对保守，但其调控的生物学功能因菌而异。

Abstract:

Xanthomonas represents a range of bacterial species that cause diseases in a variety of crops. They produce and use DSF (Diffusible signaling factor)-family quorum sensing (QS) signal to sense cell population to regulate the expression of virulence genes. At post-logic growth phase, the levels of DSF-family signal decreased rapidly, indicating a naturally occurring signal turnover phenomenon in Xanthomonas. The expression levels of rpfB that encodes a putative fatty acyl CoA ligase, significantly increased at logarithmic growth phase. Deletion of rpfB significantly increased the production of DSF-family signal. Therefore, RpfB is involved in the degradation of DSF-family signals, including Xcc to exit from the quorum sensing phase at post-QS phase. DSF-family signal negatively regulates rpfB expression via rpfC/rpfG two-component signaling system, cyclic di-GMP and the global regulator Clp. The RpfB-dependent naturally DSF turnover system is present in a range of bacterial species, representing a conserved mechanism for QS signal turnover. However, the RpfB-regulated biological roles differ from species to species.