LuxR-Type Regulator AclR1 of Azorhizobium caulinodans Regulates Cyclic di-GMP and Numerous Phenotypes in Free-Living and Symbiotic States
LuxR-Type Regulator AclR1 of Azorhizobium caulinodans Regulates Cyclic di-GMP and Numerous Phenotypes in Free-Living and Symbiotic States
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Azorhizobium caulinodans 的 LuxR 型调节因子 AclR1 调节自由生活和共生状态下的循环二 GMP 和众多表型
DOI：
10.1094/mpmi-10-19-0306-r
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发表时间：
2020-03-01
影响因子：
3.5
通讯作者：
Hu, Xiaoke
中科院分区：
文献类型：
--
作者：
Liu, Wei;Li, Yan;Hu, Xiaoke
LuxR型调控因子在细菌转录调控中发挥着重要作用，并控制着多种生物学过程。基因组序列分析表明，茎瘤固氮根瘤菌ORS571中存在7种LuxR型调控因子。茎瘤固氮根瘤菌ORS571无论是在自由生活状态还是与宿主喙荚田菁共生时，都是一种重要的固氮细菌。然而，这些调控因子的作用机制仍不明确。在本研究中，我们鉴定出一种LuxR型调控因子，其N端含有一个与cheY同源的接收（REC）结构域，并将其命名为AclR1。有趣的是，系统发育分析显示，AclR1与MalT/GerE/FixJ/NarL家族蛋白具有相对较近的进化关系。对自由生活状态下aclR1缺失突变体（ΔaclR1）的功能分析表明，AclR1对细胞运动性和絮凝起正调控作用，但对胞外多糖产生、生物被膜形成以及第二信使环二鸟苷酸（c - di - GMP）相关基因表达起负调控作用。在共生状态下，ΔaclR1突变体在宿主植物上的竞争性定殖和结瘤存在缺陷。这些结果表明，AclR1能赋予细菌有效竞争共生结瘤的能力。总体而言，我们的研究结果表明，含REC结构域的LuxR型调控因子AclR1在细菌自由生活状态和与宿主植物共生过程中对众多表型均有调控作用。
LuxR-type regulators play important roles in transcriptional regulation in bacteria and control various biological processes. A genome sequence analysis showed the existence of seven LuxR-type regulators in Azorhizobium caulinodans ORS571, an important nitrogen-fixing bacterium in both its free-living state and in symbiosis with its host, Sesbania rostrata. However, the functional mechanisms of these regulators remain unclear. In this study, we identified a LuxR-type regulator that contains a cheY-homologous receiver (REC) domain in its N terminus and designated it AclR1. Interestingly, phylogenetic analysis revealed that AclR1 exhibited relatively close evolutionary relationships with MalT/GerE/FixJ/NarL family proteins. Functional analysis of an aclR1 deletion mutant (Delta aclR1) in the free-living state showed that AclR1 positively regulated cell motility and flocculation but negatively regulated exopoly-saccharide production, biofilm formation, and second messenger cyclic diguanylate (c-di-GMP)-related gene expression. In the symbiotic state, the Delta aclR1 mutant was defective in competitive colonization and nodulation on host plants. These results suggested that AclR1 could provide bacteria with the ability to compete effectively for symbiotic nodulation. Overall, our results show that the REC-LuxR-type regulator AclR1 regulates numerous phenotypes both in the free-living state and during host plant symbiosis.