Nasser W, Bouillant M L, Salmond G, Reverchon S
Laboratoire de Génétique Moléculaire des Microorganismes et des Interactions Cellulaires, UMR-CNRS 5577, INSA, Villeurbanne, France.
Mol Microbiol. 1998 Sep;29(6):1391-405. doi: 10.1046/j.1365-2958.1998.01022.x.
The plant pathogen Erwinia chrysanthemi produces three acyl-homoserine lactones (acyl-HSLs). One has been identified as N-(3-oxohexanoyl)-homoserine lactone (OHHL), and the two others were supposed to be N (hexanoyl)-homoserine lactone (HHL) and N-(decanoyl)-homoserine lactone (DHL). The genes for a quorum-sensing signal generator (expI) and a response regulator (expR) were cloned. These genes are convergently transcribed and display high similarity to the expI-expR genes of Erwinia carotovora. ExpI is responsible for both OHHL and HHL production. Inactivation of expl had little effect on pectinase synthesis in E. chrysanthemi, as expression of only two of the pectate lyase genes, pelA and pelB, was decreased. E. chrysanthemi expR mutants still produced acyl-HSL and pectinases. However, gel shift and DNAse I footprinting experiments showed that the purified E. chrysanthemi ExpR protein binds specifically to the promoter regions of the five major pel genes. Addition of OHHL modified the ExpR-DNA bandshift profiles, indicating that ExpR interacts with OHHL and binds to DNA in different ways, depending on the OHHL concentration. Localization of the ExpR binding sites just upstream of promoter regions suggests that ExpR functions as an activator of pel expression in the presence of OHHL. The absence of a phenotype in expR mutants strongly suggests that at least an additional interchangeable ExpR homologue exists in E. chrysanthemi. Finally, transcription of expI::uidA and expR::uidA fusions is dependent on the population density, suggesting the existence of a quorum-sensing hierarchy in E. chrysanthemi. These results suggest that the expI-expR locus is part of a complex autoregulatory system that controls quorum sensing in E. chrysanthemi.
植物病原菌菊欧文氏菌可产生三种酰基高丝氨酸内酯（酰基-HSLs）。其中一种已被鉴定为N-（3-氧代己酰基）-高丝氨酸内酯（OHHL），另外两种推测为N-（己酰基）-高丝氨酸内酯（HHL）和N-（癸酰基）-高丝氨酸内酯（DHL）。克隆了群体感应信号发生器（expI）和反应调节因子（expR）的基因。这些基因反向转录，且与胡萝卜软腐欧文氏菌的expI-expR基因具有高度相似性。ExpI负责OHHL和HHL的产生。expI失活对菊欧文氏菌中果胶酶的合成影响不大，因为只有果胶酸裂解酶基因中的pelA和pelB两个基因的表达有所降低。菊欧文氏菌expR突变体仍能产生酰基-HSL和果胶酶。然而，凝胶迁移和DNA酶I足迹实验表明，纯化的菊欧文氏菌ExpR蛋白能特异性结合五个主要果胶酸裂解酶基因的启动子区域。添加OHHL会改变ExpR-DNA条带迁移图谱，表明ExpR与OHHL相互作用，并根据OHHL浓度以不同方式结合DNA。ExpR结合位点位于启动子区域上游，这表明在OHHL存在的情况下，ExpR作为果胶酸裂解酶表达的激活因子发挥作用。expR突变体中无表型这一现象强烈表明，菊欧文氏菌中至少存在一种额外的可互换ExpR同源物。最后，expI::uidA和expR::uidA融合基因的转录取决于群体密度，这表明菊欧文氏菌中存在群体感应层级。这些结果表明，expI-expR基因座是控制菊欧文氏菌群体感应的复杂自动调节系统的一部分。
