Function and Regulation of the Bradyrhizobium Japonicum nolA Gene

最近的研究已经确定了几个大家族的原核生物全局调节。PI实验室的研究结果表明，转录调节蛋白的LysR、双组分和MerR家族成员调节日本慢生根瘤菌nod基因的表达。日本芽孢杆菌nod基因表达的调控可能为探索这些全球调控系统之间的相互作用提供了一个有趣而有用的模型系统。这个项目的重点是MerR同源物，NolA。最近的研究结果表明，该蛋白是抑制nod基因表达以响应各种新的信号分子的核心参与者。NolA通过诱导NodD2抑制nod基因的表达来调节其抑制作用。PI实验室的结果表明，NolA的表达对日本芽孢杆菌细胞内产生的四聚体Nod信号水平有响应。因此，NolA是控制nod基因表达的独特反馈调控回路的一个组成部分。Nol1A的表达是由细胞密度因子（CDF，一种糖基化的类黄酮）和植物产生的被几丁质酶处理破坏的信号诱导的。本研究项目的目标是：1。确认CDF的化学结构，探索其活性，并调查其他细菌是否存在这种新型的群体感应分子；2. 2 .结合基因组学和诱变方法鉴定与NolA作用有关的其他基因；分离并化学表征了nolA表达的几丁质样植物诱导剂。这些研究将阐明NolA在nod基因表达中的作用。该研究结果与其他正在进行的研究相结合，将对日本芽孢杆菌中nod基因的表达有一个更全面的了解，并可能作为其他复杂调控系统的范例，其中全球调控网络影响单个操纵子的表达。日本芽孢杆菌与大豆共生是探索寄主与共生体间细胞信号通路的重要模型系统。这项工作的最终目标是更清楚地了解参与细胞代谢全局调节的调节机制的整合。

Recent research has identified several large families of prokaryotic global regulators. Results from the PI's laboratory have shown that members of the LysR, two-component, and MerR families of transcriptional regulatory proteins regulate Bradyrhizobium japonicum nod gene expression. Regulation of nod gene expression in B. japonicum may represent an interesting and useful model system in which to explore the interactions between these global regulatory systems. The focus of this project is the MerR orthologue, NolA. Recent results show that this protein is a central player in the repression of nod gene expression in response to a variety of novel signal molecules. NolA mediates its repressive effects by induction of NodD2, which represses nod gene expression. Results from the PI's laboratory indicate that NolA expression is responsive to the level of intracellular, tetrameric Nod signal produced in B. japonicum. Therefore, NolA is a component of a unique feedback, regulatory loop that controls nod gene expression. Nol1A expression is induced by a cell density factor (CDF, a glycosylated flavonoid) and a plant-produced signal that is destroyed by chitinase treatment. The objectives of this research project are to 1. confirm the chemical structure of the CDF, explore its activity, and survey other bacteria for the presence of such a novel, quorum sensing molecule; 2. identify other genes involved in NolA action using a combination of genomic and mutagenic approaches and 3. isolate and chemically characterize the chitin-like plant inducer of nolA expression. These studies should clarify the role of NolA in nod gene expression. The results obtained, when added to other on-going research, should give a more complete picture of nod gene expression in B. japonicum and may serve as a paradigm for other complex regulatory systems where global regulatory networks impinge on the expression of a single operon. The B. japonicum-soybean symbiosis is an important model system for exploring the cell signaling pathways between host and symbiont. The ultimate goal of this work is a clearer understanding of the integration of regulatory mechanisms involved in the global regulation of cellular metabolism.