Nitrogen-fixing root nodules result from an endosymbiotic association between Rhizobium bacteria and specific legume host plants. Dr. Cooper will utilize cellular and molecular genetic approaches to investigate early events in the development of root nodules in the Rizobium meliloti-Medicago truncatula symbiosis. The specific goals of this proposal are: 1) to clone and characterize the nodulin genes expressed early in nodule development, with particular attention paid to (hydroxy)proline- rich cell wall glycoprotein genes; 2) to examine the spatial and temporal patterns of early symbiotic gene expression at both the protein and nucleic acid levels; and 3) to use reporter gene fusions to identify the cis-acting regulatory sequences responsible for the observed patterns of gene expression, and to begin characterizing the signal molecules used by Rhizobium to regulate plant development. Results of these studies will provide new tools for the molecular genetic dissection of nodule development and plant-microbe interactions. %%% The mechanisms regulating the association of nitrogen fixing bacteria with the roots of compatible plants is a problem of interest both as a basic science question of how organisms interact and affect each other and a problem with great agricultural economic and ecological interest. Plants which are susceptible to this mode of interaction do not require the same addition of nitrogenous fertilizer for their growth.
