Summaries of Legume Genomics Projects from around the Globe. Community Resources for Crops and Models

Genomic research has and will continue to revolutionize plant biology. It is clear that the adoption of Arabidopsis as a model species has done much to speed the development of plant genomics and to hasten our increased understanding of basic plant biology. However, Arabidopsis is not an “omniscient” model because this plant does not encompass all of the diverse physiological, developmental, and environmental processes seen throughout the plant kingdom. Thus, to study these other processes and to bring the genomic revolution to crop species, additional genomic resources must be developed in other plants. Over the past several years, this realization has led to the adoption of the model species concept to the study of legumes. Unlike Arabidopsis, legumes develop important and interesting symbioses with nitrogen (N)-fixing rhizobia and with mycorrhizal fungi. They also exhibit interesting differences in secondary metabolism, pod development, and other processes that cannot be adequately modeled with Arabidopsis. The impetus for the development of legume models has come primarily from researchers interested in the rhizobium-legume symbiosis. Because of this, two models, not one, have been developed: Lotus japonicus and Medicago truncatula. In reality, these two models have evolved due to the energy of their proponents but, scientifically, they can also be justified because they exhibit two developmental systems for nodulation as well as other differences. L. japonicus forms determinate nodules, in which the root subepidermal cortical cells initiate nodule formation and a persistent, terminal nodule meristem does not develop. In contrast, M. truncatula nodules initiate from the division of inner cortical cells and continue to grow from a terminal, persistent meristem. As can be seen by the summaries below, both legume model species are now well established with a large number of laboratories involved. Therefore, in the long run, legume biology can only benefit by a comparison of the results between these models and legume crop plants. In contrast to the effort focused on the legume models, with the possible exception of soybean (Glycine max), significantly smaller efforts exist to study the genomics of legume crop species. This is unfortunate because it remains to be seen just how much of the information developed from legume models can be directly applied to the improvement of legume crops. It is clear that legume biology is rapidly undergoing a revolutionary transformation due to the application of genomic methods. The future is exceedingly bright, and one would expect rapid progress in our understanding of basic plant processes and the unique aspects of legume physiology and development. The edited summaries below represent the currently funded genomic activities focused on legume models and crops. For convenience, these are listed by relevant species, although similar trends and interests are apparent throughout.