The legume family is one of the most important groups of plants worldwide because they have been fundamental to development of modern agricultural systems. Agronomically important members include soybean and rice in Asia, and maize and beans in the Americas. Legumes are also the third largest family of flowering plants. On a worldwide basis, this plant family contributes 33% of humankind's protein intake, while also serving as an important source of fodder and forage for animals, and of edible and industrial oils. Legumes are also distinguished by their unique property of symbiotic nitrogen fixation, providing one of the major sources of available nitrogen in the biosphere. In the US alone, legumes are grown on over 80 million acres, where they fix approximately 6 million metric tons of nitrogen worth an estimated $4.5 billion.
In response to the need for a tractable genetic system in legumes, scientists have developed Medicago truncatula as a model species for study of biological and agronomic issues important to legumes. Of particular significance, Medicago is amenable to efficient molecular, genetic and reverse-genetic analyses, unlike the major crop legumes.
This project involves the large-scale analysis of the genome of Medicago. A map of the organization of genes (comparative genomics), of their functions in legume biology (functional genomics), and analysis and public distribution of the data by means of computational tools (bioinformatics), are the emphases of this project. Recent results from this research team document the first indications of conserved genome structure between Medicago and crop legumes, and between Medicago and the well-characterized model plant Arabidopsis thaliana. We have described the genomic architecture of resistance gene analogs and discovered new lineages of legume resistance genes. We have contributed to the development of a public Expressed Sequence Tag (EST) resource containing in excess of 127,000 sequences, and created publicly accessible databases to relate this information to other scientists and to the public. Already this information has accelerated the pace of discovery and characterization of agronomically important legume genes and traits, in both Medicago and crop legume species.
The goal of this research is to extend these analyses by contributing to a multi-institutional, international effort to develop a complete gene inventory and functional analysis of the Medicago genome. The specific objectives of this research include (1) creating a comprehensive physical map of the genome, (2) assaying the coordinate expression of thousands of genes under conditions of (a) plant development, (b) interactions with microorganisms, and (c) nutrient stress, and (3) continuing to implement and improve publicly accessible database activities.
The long-term impact of this research will be to integrate genetic and functional information across legumes, and thereby expand opportunities for basic and applied research in economically important legume species. This research will allow scientists to compare genes of agronomic and scientific interest in Medicago and the related crop legumes. This knowledge will enable more efficient cloning and characterization of valuable genes and traits, such as disease resistance and crop productivity, and it will ultimately facilitate the development of improved crop varieties. The database of expressed genes generated by this research will enable the detailed analysis of the role of specific genes in plant growth and development. Many of the genes identified in the course of this research will become the focus of crop improvement strategies and of continued scientific investigation by legume biologists. The proposed work benefits enormously from previous NSF-sponsored research on the model plant Arabidopsis. Likewise, completion of the project will benefit not only research on legumes, but the broader scientific community as well.
