RESEARCH PGR: An interdisciplinary approach to deciphering molecular signaling pathways controlling plant-symbiont associations in legumes and cereals.

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Part 1: Non-technical abstractThe roots of crop plants contain important microorganisms that allow the plants and microbes to satisfy their nutritional needs. The relationship between these two very different types of organisms is called symbiotic because both partners benefit from the association. The plant converts sunlight and carbon dioxide into sugars and other organic compounds that are supplied to the microbes in the roots. The microbes provide phosphate and nitrogen to the plant in forms that the plant can readily ingest. These symbiotic associations permit the growth of some crops without added fertilizer. For example, plants are unable to convert gaseous nitrogen in the atmosphere into a reduced form that can be incorporated into the proteins, vitamins and other critical biomolecules that allow them to germinate, develop and grow. Certain crops, such as the legumes (e.g., beans, peas and alfalfa) harbor nitrogen-converting bacteria within specialized structures in their roots that provide this reduced nitrogen to the plant. Most crops do not have these bacteria and must rely on the application of nitrogen fertilizer for optimal growth. This project seeks to obtain a molecular understanding of this symbiotic association between plant and microbes, with a long-term goal of enabling such an association in non-leguminous crops like corn and wheat, which currently require extensive fertilization to sustain crop yield. A broader impact of this project is a summer Plant Proteomics Workshop, which provides training in proteomic and genomic profiling to the entire plant research community.Part 2: Technical abstractThis project seeks to profile the early molecular events in the recognition of and response to symbiotic microbes (nitrogen-fixing rhizobia and arbuscular mycorrhizal fungi) by the model legume crop, Medicago truncatula and the model monocot, rice. This approach will enable a comparison at the molecular level of the mechanisms by which these two crop groups recognize their beneficial microbes. The analysis of the shared and distinct chemical and genetic factors in these two systems should provide tools and information to enable the engineering of beneficial associations between cereal crops (e.g., rice, corn, wheat) and nitrogen-fixing rhizobia. The specific aims are (1) the identification of host proteins modified by phosphorylation, acetylation or ubiquitinylation in first hour following signal reception, and validation of potentially active candidates from this and from the previous project award period, (2) the integration of proteomic and transcriptomic responses into networks that can be compared in the two species, using informatics and computational modeling, and (3) a high-throughput screen for symbiosis factors using a newly developed chemical genomics chip system. This project will expand a Plant Proteomics Workshop for training in the latest large-scale proteomic and genomic profiling technologies.