How Does the Plant Say-No More?: A Molecular Genetic Approach to Nodule Number Regulation

固氮菌对豆科植物根部的定植受共生伙伴之间一系列复杂的相互作用的调节。终点是一个被称为根瘤的特殊器官，它由植物的根形成，用来容纳细菌。为了换取植物提供的碳，细菌从空气中为植物提供氮，使豆类在没有土壤氮的情况下具有独特的生长能力。本项目以植物共生控制为重点，以遗传模式种紫花苜蓿为寄主，中华根瘤菌为细菌共生体。将研究该植物调节其形成的结核数量的机制。PI表明，根瘤数量的调节是通过在根和茎之间传递的信号来进行的。关于根和茎是如何相互传递信号的四个问题仍然没有得到回答：什么是向茎发出的结瘤信号？是什么感知了枝条中的信号？根部信号的性质是什么？根中的信号由什么接收？将使用生理、遗传和生化方法的组合来识别信号并确定它们是如何被感知的。为此，研究人员将分析参与调节对信号反应的基因、营养物质和植物激素。目前已知的以及在这一途径中发挥作用的新基因和蛋白质将被描述为氮肥生产成本高，过度施肥是地下水污染的来源，使豆类在缺乏土壤氮的情况下生长的独特能力非常适合农业。由于根瘤数量调控途径也参与根的生长，因此该项目的结果对于未来农业中的结瘤操作以及揭示所有植物如何协调地上部和根的生长是至关重要的。该项目将培养两名博士生和四名本科生，同时为几名高中生提供暑期研究机会。首席调查员将通过既定的大学项目教授研究伦理方面的最佳做法，并在面向公众的科学会议和大学项目中传播这一项目的结果，从而开展外联活动。

The colonization of roots of plants in the legume family by nitrogen-fixing bacteria is regulated by a complex series of interactions between the symbiotic partners. The endpoint is a specialized organ called a nodule, which is formed by the plant roots to house the bacteria. In exchange for carbon provided by the plant, the bacteria provide the plant with nitrogen from the air, allowing legumes the unique ability to grow in the absence of soil nitrogen. This project focuses on the plant's control of the symbiosis, with the genetically enabled model species Medicago truncatula as the plant host and Sinorhizobia as the bacterial symbiont. The mechanisms by which the plant regulates the number of nodules it forms will be studied. The PI has shown that regulation of nodule number occurs by way of signals that travel between roots and shoots. Four questions about how the root and shoot signal to each other remain unanswered: What is the nodulation signal to the shoot? What perceives the signal in the shoot?What is the nature of the signal to the root? What receives the signal in the root? A combination of physiological, genetic and biochemical approaches will be employed to identify the signals and determine how they are perceived. Towards this end investigators will analyze the genes, nutrients and plant hormones involved in regulating responses to the signals. Currently-known as well as new genes and proteins that function in this pathway will be characterized Nitrogen fertilizer is costly to produce and excessive fertilizer application is a source of groundwater pollution, making the unique ability of legumes to grow in the absence of soil nitrogen highly desirable for agriculture. Because the nodule number regulatory pathway is also involved in root growth, the results of this project are critical to future manipulation of nodulation in agriculture and for revealing how all plants coordinate shoot and root growth. The project will train two doctoral students and four undergraduates, while providing summer research opportunities to several high school students. The lead investigator will engage in outreach by teaching best practices in research ethics through established university programs and disseminating the results of this project at scientific meetings and university programs targeted to the general public.