The cin and rai Quorum-Sensing Regulatory Systems in Rhizobium leguminosarum Are Coordinated by ExpR and CinS, a Small Regulatory Protein Coexpressed with CinI
The cin and rai Quorum-Sensing Regulatory Systems in Rhizobium leguminosarum Are Coordinated by ExpR and CinS, a Small Regulatory Protein Coexpressed with CinI
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DOI：
10.1128/jb.01650-08
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发表时间：
2009-05-01
影响因子：
3.2
通讯作者：
Downie, J. Allan
中科院分区：
文献类型：
--
作者：
Edwards, Anne;Frederix, Marijke;Downie, J. Allan
为了了解豆科根瘤菌raiI-raiR群体感应系统是如何调节的，我们鉴定了具有降低的RaiI-制造的N-酰基高丝氨酸内酯（AHLs）水平的突变体。一个LuxR型调节器，ExpR，需要raiR的表达，和RaiR需要诱导raiI。由于在cinI和cinR群体感应突变体中raiR（和raiI）表达也减少，我们认为CinI制造的AHLs可能激活ExpR以诱导raiR。然而，添加CinI-制造的AHLs并不诱导raiR在cinI突变体中的表达。在cinI和cinR突变体中raiR表达的减少是由于cinI下游cinS表达的缺乏。cinS编码一个67个残基的蛋白质，与CinI偶联，cinS在expR的下游作用，诱导raiR。克隆到R.豆锈菌引起的菌落结构异常崩溃，这是延迟的expR突变。表型看起来像是胞外多糖（EPS）完整性的丧失; cinI、cinR、cinS和expR的突变都降低了编码EPS聚糖酶的CINB的表达，CINB的突变消除了克隆的cinS对菌落形态的影响。我们得出结论，CinS和ExpR的作用，以增加PlyB水平，从而影响细菌表面。CinS在其他根瘤菌中是保守的，包括Rhizobium etli;先前观察到的cinI和cinR突变减少该菌株群集的效果主要是由于缺乏CinS，而不是缺乏CinI产生的阿勒。我们的结论是，CinS介导的群体感应调节，因为它与阿勒合酶共调节，并表明其调节作用可以发生在没有AHLs。
To understand how the Rhizobium leguminosarum raiI-raiR quorum-sensing system is regulated, we identified mutants with decreased levels of RaiI-made N-acyl homoserine lactones (AHLs). A LuxR-type regulator, ExpR, is required for raiR expression, and RaiR is required to induce raiI. Since raiR (and raiI) expression is also reduced in cinI and cinR quorum-sensing mutants, we thought CinI-made AHLs may activate ExpR to induce raiR. However, added CinI-made AHLs did not induce raiR expression in a cinI mutant. The reduced raiR expression in cinI and cinR mutants was due to lack of expression of cinS immediately downstream of cinI. cinS encodes a 67-residue protein, translationally coupled to CinI, and cinS acts downstream of expR for raiR induction. Cloned cinS in R. leguminosarum caused an unusual collapse of colony structure, and this was delayed by mutation of expR. The phenotype looked like a loss of exopolysaccharide (EPS) integrity; mutations in cinI, cinR, cinS, and expR all reduced expression of plyB, encoding an EPS glycanase, and mutation of plyB abolished the effect of cloned cinS on colony morphology. We conclude that CinS and ExpR act to increase PlyB levels, thereby influencing the bacterial surface. CinS is conserved in other rhizobia, including Rhizobium etli; the previously observed effect of cinI and cinR mutations decreasing swarming in that strain is primarily due to a lack of CinS rather than a lack of CinI-made AHL. We conclude that CinS mediates quorum-sensing regulation because it is coregulated with an AHL synthase and demonstrate that its regulatory effects can occur in the absence of AHLs.