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.
