Quorum-Sensing and Growth Control in Rhizobium sp. NGR234

根瘤菌的群体感应和生长控制。

• 批准号: 0223724
• 负责人: William Fuqua
• 金额: $ 30万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-09-01 至 2006-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0223724&HistoricalAwards=false
• 关键词: Quorum; Sensing; Growth; Control; Rhizobium

Gram-negative bacteria within the Proteobacteria group commonly use acylated homoserine lactones (acyl-HSLs) as molecular signals in the process of quorum sensing (QS). Quorum-sensing bacteria release diffusible signal molecules that accumulate with increasing cell number, eventually triggering adaptive responses. Regulatory proteins of the LuxI and LuxR families are usually required for synthesis of, and response to acyl-HSLs, respectively. Diffuse populations of cells generally produce a constant, low level of acyl-HSLs, and these rapidly diffuse out of cells down their concentration gradient. Elevated population density increases the relative acyl-HSL concentration, eventually fostering interaction of the signals with LuxR-type proteins, which in turn, control the transcription of target genes. Although this basic mechanism is well conserved, the context of QS regulation and the cellular functions under its control are highly variable among different bacteria. This project focuses on the regulatory context of a LuxI-LuxR-type QS system employed by the nitrogen-fixing plant symbiont Rhizobium sp. NGR234, its mechanism of action, and its effect on cellular growth rate. NGR234 incites the formation of nitrogen-fixing, symbiotic nodules on the roots of a wide range of leguminous plants. The molecular basis of this promiscuous host interaction has been extensively studied. Many of the functions that orchestrate the plant interaction are carried on the 536 kb pNGR234a plasmid. The pNGR234a plasmid also carries a large cluster of genes homologous to plasmid replication (rep) and conjugal transfer (trb/tra) genes from other bacteria. The rep/trb/tra cluster includes a LuxI-LuxR-type regulatory pair, TraI and TraR, and the additional QS regulator TraM. TraI synthesizes 3-oxo-octanoyl-L-homoserine lactone and TraR interacts with this acyl HSL to regulate tra/trb and rep operon expression. TraM acts to inhibit TraR through formation of an anti-activation complex. A molecular genetic approach is being employed to study the QS mechanism in NGR234. The regulatory signals and pathways that control traR expression will be investigated to determine the conditions that foster QS. Based on analogous systems, the host plant is likely to play a role in this regulation. The QS-regulated pNGR234a genes under TraR control will be identified and the mechanism by which TraR controls their expression elucidated. Lastly, control of cellular growth rate by QS, a common QS regulatory target among several Rhizobium species, will be examined. Findings generated from the research project will provide fundamental information on cell-to-cell communication in an important plant symbiont, and the role of this communication in its highly plastic host interactions. More generally, these studies will add to the understanding of how cell-to-cell communication directly and indirectly influences interactions with host organisms, and enables quorum-sensing microbes to balance their physiological activity with the host environment.The bacterium Rhizobium sp. NGR234 uses cell-to-cell communication during its symbiotic relationships with higher plants. The research project examines the biochemical and genetic mechanisms underlying this intercellular communication, and its influence on the interaction of this bacterium and host plants. The findings generated from this work will provide fundamental knowledge required to take advantage of these bacterial communication systems, for combating infectious disease in plants and animals, as well as promoting beneficial microbial interactions.

在蛋白质杆菌组中，革兰氏阴性细菌通常在Quorum Sensing（QS）的过程中使用酰基化的同氨酸内酯（酰基-HSL）作为分子信号。 群体感应细菌释放随着细胞数量增加而积聚的扩散信号分子，最终触发适应性反应。 通常需要分别对Luxi和LuxR家族的调节蛋白进行合成和对酰基-HSL的反应。 细胞的弥散群通常会产生恒定的低水平酰基-HSL，这些细胞群体迅速从细胞降低其浓度梯度。 升高的种群密度增加了相对的酰基-HSL浓度，最终促进了信号与LuxR型蛋白的相互作用，从而控制靶基因的转录。 尽管这种基本机制是充分保守的，但QS调节的背景和其控制下的细胞功能在不同细菌之间差异很大。 该项目着重于由氮固定植物共生型根瘤菌所采用的luxi-luxr型QS系统的调节背景。 NGR234，其作用机理及其对细胞生长速率的影响。 NGR234促进了氮固定，共生结节在各种豆科植物的根上的形成。 这种混杂宿主相互作用的分子基础已经进行了广泛的研究。 编排植物相互作用的许多功能都在536 kb PNGR234A质粒上携带。 PNGR234a质粒还带有来自其他细菌的质粒复制（REP）和词传递（TRB/TRA）基因的大量基因。 REP/TRB/TRA群集包括Luxi-luxr型调节对，TRAI和TRAR，以及其他QS调节器电车。 TRAI合成了3-氧基二氧酰基-L-霍森内酯和Trar与该酰基HSL相互作用，以调节TRA/TRB和REP操纵子的表达。 电车通过形成抗激活复合物来抑制TRAR。 正在采用一种分子遗传方法来研究NGR234中的QS机制。 将研究控制TRAR表达的监管信号和途径，以确定促进QS的条件。 基于类似的系统，宿主工厂可能在该法规中发挥作用。 将鉴定在Trar控制下的QS调节的PNGR234A基因，以及Trar控制其表达阐明的机制。 最后，将检查通过QS控制细胞生长速率，这是几种根茎物种中常见的QS调节靶标。 研究项目产生的发现将提供有关重要植物共生体中细胞间通信的基本信息，以及这种通信在其高度塑料宿主相互作用中的作用。 更笼统地，这些研究将增加对细胞间通信如何直接和间接影响与宿主生物的相互作用的理解，并使群体感应微生物与宿主环境平衡其生理活性。细菌根瘤菌SP。 NGR234在与较高植物的共生关系期间使用细胞对细胞通信。 该研究项目研究了这种细胞间通信的基础的生化和遗传机制，及其对该细菌和宿主植物相互作用的影响。 这项工作产生的发现将提供基本知识，以利用这些细菌通信系统，以打击动植物中的传染病以及促进有益的微生物相互作用。