The Wisconsin Plant Symbiosis Group is an interdisciplinary research team that develops and applies state-of-the-art genomic technologies for profiling early molecular events controlling the recognition of symbiotic microbes (nitrogen-fixing rhizobia and arbuscular mycorrhizal fungi) by the model legume crop, Medicago truncatula (Medicago). This renewal proposal aims to expand on previous work, particularly in the area of discovery and validation of quantitative proteomic measurements of post-translational modifications, with new comparative experiments performed with a second model crop species, Oryza sativa (rice), a member of the cereals that associate efficiently with arbuscular mycorrhizal fungi but not with rhizobia. Thus, a comparison of the molecular mechanisms by which these two crop groups recognize their beneficial microbes will help us understand how they evolved and identify new strategies, both genetic and chemical, by which they may be modified. In the long term, knowledge from this unique project will help the research community engineer more intimate associations between cereal crops (e.g., rice, corn, wheat) and nitrogen-fixing rhizobia. Thus, the results of this research may help reduce the large amount of environmentally deleterious fertilizer that is currently applied to corn and other crops.