Regulation of ureide metabolism in legumes

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Nitrogen fixation in legumes is an important natural mechanism in the global nitrogen cycle. Legumes can form symbioses with soil bacteria to develop specialized root structures called nodules.   The plant supplies carbon, obtained through photosynthesis, to the bacteria and the bacteria convert atmospheric nitrogen, a  fundamental component of protein, DNA and other biomolecules, to a form usable by the plant.  This process is called nitrogen fixation.  In agricultural legumes, this provides an important mechanism to supply nitrogen to the diets of humans and livestock and requires far less artificial nitrogen fertilization.In soybean and related legumes, fixed nitrogen moves as ureides from the nodules to leaves, pods and seeds, where they are then broken down, allowing the nitrogen to be utilized.  When water becomes limiting, ureides build up and nitrogen fixation ceases.  This process is extremely sensitive to water limitation, but we do not yet understand why.  The overall theme of the research program will be molecular and biochemical regulation of nitrogen metabolism in legumes.  The focus will be ureide metabolism and nitrogen fixation. Specific objectives include the identification of genes involved in ureide metabolism and determining how ureide catabolism is regulated.  The research program will integrate plant physiology, biochemistry and molecular biology to augment our understanding of ureide metabolism in legume species.  Currently, regulation of ureide metabolism is poorly characterized and this process has not been examined in any legume crop species at the molecular level.  As nitrogen fertilizer prices increase in response to rising energy costs, legume production becomes more attractive, both as crops with potential for biofuels, as well as those requiring less artificial nitrogen fertilizer.  Understanding the regulatory mechanisms controlling ureide catabolism and nitrogen fixation in response to abiotic stresses, particularly those that may be brought on by climate change, will be critical in improving legume production through management practices, breeding or biotechnology.