MOLECULAR-BASIS OF SYMBIOSIS BETWEEN RHIZOBIUM AND LEGUMES

Access to mineral nitrogen often limits plant growth, and so symbiotic relationships have evolved between plants and a variety of nitrogen-f ixing organisms, These associations are responsible for reducing 120 m illion tonnes of atmospheric nitrogen to ammonia each year, In agricul ture, independence from nitrogenous fertilizers expands crop productio n and minimizes pollution of water tables, lakes and rivers. Here we p resent the complete nucleotide sequence and gene complement of the pla smid from Rhizobium sp. NGR234 that endows the bacterium with the abil ity to associate symbiotically with leguminous plants, In conjunction with transcriptional analyses, these data demonstrate the presence of new symbiotic loci and signalling mechanisms. The sequence and organiz ation of genes involved in replication and conjugal transfer are simil ar to those of Agrobacterium, suggesting a recent lateral transfer of genetic information.