Azorhizobium caulinodans Chemotaxis Is Controlled by an Unusual Phosphorelay Network
Azorhizobium caulinodans Chemotaxis Is Controlled by an Unusual Phosphorelay Network
复制标题
固氮根瘤菌趋化性由不寻常的磷中继网络控制
DOI：
10.1128/jb.00527-21
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发表时间：
2022-02-01
影响因子：
3.2
通讯作者：
Bourret, Robert B.
中科院分区：
文献类型：
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作者：
Kennedy, Emily N.;Barr, Sarah A.;Bourret, Robert B.
固氮菌是一种在豆科植物田菁上形成根瘤的固氮菌。这种在农业上具有重要意义的共生关系在低地水稻种植中很重要，并允许在洪水条件下进行固氮。趋化性在细菌在根际的定植中起着重要作用。植物根部释放细菌能感觉到的化合物，引发沿浓度梯度向根部的趋化作用。这使游动细菌在根面定植过程中具有显著的竞争优势。虽然植物相关的细菌基因组通常编码多个趋化系统，但茎突假单胞菌似乎只编码一个。其基因组上的ChE簇包含CheA、Chew、cheY2、Cheb和Cher。另外两个趋化基因cheY1和cheZ独立于ChE操纵子。CheY1和CheY2都参与趋化作用，其中CheY1是主要的信号蛋白。A.caulinodans Chea包含一组不寻常的C-末端结构域：在更常见的单个咀嚼样结构域之后是一对咀嚼状/接收器对(称为W2-Rec)。W2-Rec对趋化作用和CHEA功能均有影响。我们发现磷酰基从CheA转移到CheY2，而不是转移到W2-Rec或CheY1，这似乎参与了鞭毛马达结合。此外，我们观察到与CheY2和W2-Rec相比，CheY1上的磷酰基稳定性增加。最后，CHEZ比CheY1更能促进CheY2的去磷酸化，但对W2-Rec的去磷酸化速率没有影响。这一磷转移反应网络突显了一个以前未被描述的趋化反应调节方案。重要的趋化作用使细菌能够向营养物质移动，而不是环境中的毒素。趋化运动比非特异性运动提供了竞争优势。Chey是趋化反应的重要介质，磷酸化和非磷酸化形式的Chey与鞭毛运动不同地相互作用，改变游泳行为。先前建立的Chey去磷酸化方案包括磷酸酶的作用和/或将磷酸基转移到作为接收器的另一个接收域。在这里，我们提出了一种协同机制，在该机制中，CheA、CheY2和CHEZ的HPT结构域作为一个双汇聚系统一起发挥作用，以快速重新启动趋化信号。据我们所知，这一机制与以前评估过的任何机制都不同。趋化系统同时利用受体和HPT结构域作为磷酸盐汇，可能存在于其他细菌物种中。
Azorhizobium caulinodans is a nitrogen-fixing bacterium that forms root nodules on its host legume, Sesbania rostrata. This agriculturally significant symbiotic relationship is important in lowland rice cultivation and allows nitrogen fixation under flood conditions. Chemotaxis plays an important role in bacterial colonization of the rhizosphere. Plant roots release chemical compounds that are sensed by bacteria, triggering chemotaxis along a concentration gradient toward the roots. This gives motile bacteria a significant competitive advantage during root surface colonization. Although plant-associated bacterial genomes often encode multiple chemotaxis systems, A. caulinodans appears to encode only one. The che cluster on the A. caulinodans genome contains cheA, cheW, cheY2, cheB, and cheR. Two other chemotaxis genes, cheY1 and cheZ, are located independently from the che operon. Both CheY1 and CheY2 are involved in chemotaxis, with CheY1 being the predominant signaling protein. A. caulinodans CheA contains an unusual set of C-terminal domains: a CheW-like/receiver pair (termed W2-Rec) follows the more common single CheW-like domain. W2-Rec impacts both chemotaxis and CheA function. We found a preference for transfer of phosphoryl groups from CheA to CheY2, rather than to W2-Rec or CheY1, which appears to be involved in flagellar motor binding. Furthermore, we observed increased phosphoryl group stabilities on CheY1 compared to CheY2 and W2-Rec. Finally, CheZ enhanced dephosphorylation of CheY2 substantially more than CheY1 but had no effect on the dephosphorylation rate of W2-Rec. This network of phosphotransfer reactions highlights a previously uncharacterized scheme for regulation of chemotactic responses.IMPORTANCE Chemotaxis allows bacteria to move toward nutrients and away from toxins in their environment. Chemotactic movement provides a competitive advantage over nonspecific motion. CheY is an essential mediator of the chemotactic response, with phosphorylated and unphosphorylated forms of CheY differentially interacting with the flagellar motor to change swimming behavior. Previously established schemes of CheY dephosphorylation include action of a phosphatase and/or transfer of the phosphoryl group to another receiver domain that acts as a sink. Here, we propose that A. caulinodans uses a concerted mechanism in which the Hpt domain of CheA, CheY2, and CheZ function together as a dual sink system to rapidly reset chemotactic signaling. To the best of our knowledge, this mechanism is unlike any that have previously been evaluated. Chemotaxis systems that utilize both receiver and Hpt domains as phosphate sinks likely occur in other bacterial species.