Symbiotic nitrogen fixation research in the postgenomics era

Nitrogen-fixing symbioses between legumes and rhizobia are important for sustainable agriculture and contribute significantly to the global nitrogen cycle. The genomes of two rhizobial species, Mesorhizobium loti and Sinorhizobium meliloti have now been completely sequenced. Hundreds of thousands of expressed sequence tags representing tens of thousands of different genes from three major legume species; soybeans Medicago truncatula and Lotus japonicus have also been deposited in the public domain. Lotus japonicus recently became the focus of a genome project that aims to sequence one third of the entire genome over the next 5 yr. With this as a backdrop, the stage is set for a renaissance in symbiosis research, which will provide new insight into the complex molecular interplay that underpins symbiotic nitrogen fixation. This review considers how functional genomics might contribute to this renaissance.