Function and Regulation of the Bradyrhizobium Japonicum nolA Gene

最近的研究已经确定了几个大的原核生物全球调控因子家族。PI的实验室结果表明，转录调控蛋白LysR、双组分和MERR家族的成员调控慢生根瘤菌nod基因的表达。日本血吸虫nod基因表达的调控可能是探索这些全球调控系统之间相互作用的一个有趣和有用的模型系统。这个项目的重点是默尔的直白，诺拉。最近的研究结果表明，该蛋白在多种新的信号分子对nod基因表达的抑制中起着中心作用。NOLA通过诱导抑制NOD基因表达的NodD2来介导其抑制作用。PI实验室的结果表明，NOLA的表达水平与日本双胞菌产生的胞内四聚体NOD信号水平有关。因此，NOLA是控制NOD基因表达的独特反馈调控环的组成部分。Nol1a的表达是由细胞密度因子(CDF，一种糖基化的黄酮类化合物)和植物产生的信号诱导的，几丁质酶处理破坏了这种信号。本研究项目的目标是：1.确定CDF的化学结构，探索其活性，并调查其他细菌中是否存在这样一种新的群体感应分子；2.结合基因组和突变方法鉴定参与NOLA作用的其他基因；3.分离并鉴定NOLA表达的几丁质样植物诱导剂。这些研究应该阐明NOLA在NOD基因表达中的作用。所获得的结果，加上其他正在进行的研究，应该会给出更完整的日本血吸虫nod基因表达的图景，并可能作为其他复杂调控系统的范例，在这些系统中，全球调控网络影响单个操纵子的表达。日本血吸虫-大豆共生是探索寄主与共生体之间细胞信号转导途径的重要模式系统。这项工作的最终目标是更清楚地了解参与全球细胞代谢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.