Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2003
Publication Date: 8/1/2003
Citation: MACHADO, D., KRISHNAN, H.B. NODD ALLELES OF SINORHIZOBIUM FREDII USDA191 DIFFERENTIALLY INFLUENCE SOYBEAN NODULATION, NODC EXPRESSION, AND PRODUCTION OF EXOPOLYSACCHARIDES. CURRENT MICROBIOLOGY. 2003. V. 47(2). P. 134-137. Interpretive Summary: Sinorhizobium fredii forms nodules on the roots of soybean plants. The nodules are specialized structures where atmospheric nitrogen is fixed by the bacterium, which in turn, is utilized by soybean plants for growth and development. This process is termed biological nitrogen fixation and it enables soybean plants to grow in nitrogen-poor soils. The ability of S. fredii to form nitrogen-fixing nodules on soybean plants is controlled by a regulatory gene, nodD1. We have studied the importance of this gene in regulating the formation of nitrogen-fixing root nodules on soybean. Information obtained from this basic study will enable manipulation of biological nitrogen fixation so that farmers can increase the yield of soybean with minimal use of nitrogen fertilizers.
Technical Abstract: All Rhizobium strains examined to date have one or multiple alleles of nodD. At least one copy of nodD and the presence of flavonoid exudates are required for nod-gene induction and nodulation. Sinorhizobium fredii USDA191 has two copies of nodD. In this study, we demonstrate that inactivation of either copy of nodD caused a reduction in basal levels of expression of nodC. Extra copies of nodD1 had no effect on the expression of nodC when compared to the wild type, but extra copies of nodD2 abolished the inducer requirement, thereby rendering nodC constitutive. A nodD1 mutant was unable to nodulate soybean cultivars 'Peking' and 'McCall'. Inactivation of nodD2 or addition of extra copies of nodD1 or nodD2 caused delayed nodulation on Peking, and reduced the number of nodules on McCall. Both nodD alleles of S. fredii USDA191 appear to be involved in regulation of exopolysaccharide production; however, nodD2 appears to be more important in this respect than nodD1.