Submitted to: Current Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/5/2001
Publication Date: 11/1/2002
Citation: RANA, D., KRISHNAN, H.B. MOLECULAR CLONING AND CHARACTERIZATION OF NODD GENES FROM RHIZOBIUM SP. SIN-1, A NITROGEN-FIXING SYMBIONT OF SESBANIA AND OTHER TROPICAL LEGUMES. CURRENT MICROBIOLOGY. 2002. V. 45(5). P. 378-382. Interpretive Summary: Green manuring refers to a practice where rapidly growing legumes like Sesban are plowed into the soil. The decomposing crop provides nutrients to the subsequent crop. A bacterium, Rhizobium sp. SIN-1, forms nodules on the roots of green manure crops. The nodules are specialized structures where atmospheric nitrogen is fixed by the bacterium, which in turn, is utilized by the legumes for its rapid growth and development. This proces is termed biological nitrogen fixation and it enables legumes to grow in nitrogen-poor soils. In this study, we isolated key regulatory genes that control nodulation on green manure legume crop. Our results provide clues to researchers and farmers seeking to improve crop management by recycling of plant nutrients to increase crop yields without the use of costly chemical fertilizers.
Technical Abstract: Rhizobium sp. SIN-1, a nitrogen-fixing symbiont of green manure crops, carries two copies of nodD genes that are located on a sym plasmid. We have isolated these two nodD genes by screening a genomic library of Rhizobium sp. SIN-1 with a nodD probe from Sinorhizobium meliloti. Nucleotide sequence analysis and the deduced amino acid sequence indicated that the nodD genes of Rhizobium sp. SIN-1 are more closely related to Rhizobium tropici and Azorhziobium caulinodans. Rhizobium sp. SIN-1 nodD1 complemented S. meliloti nodD1D2D3-negative mutant for nodulation on alfalfa but failed to complement a nodD1 mutant of S. fredii USDA191 for soybean nodulation. A hybrid nodD gene, containing the N-terminus of S. fredii USDA191 nodD1 and the C-terminus of Rhizobium sp. SIN-1 nodD1, complemented the nodD1- negative mutant of USDA191 for nodulation on soybean. Rhizobium sp. SIN-1 nodD2 was unable to complement any of the S. meliloti or S. fredii nodD mutants. Introduction of a cosmid containing the nodD2 of Rhizobium sp. SIN-1 into S. fredii USDA191 directed the synthesis of five new soluble proteins with apparent molecular mass of 66 kDa, 44 kDa, 43 kDa, 37 kDa and 27 kDa. In addition, S. fredii USDA191 carrying Rhizobium sp. SINI-1 nodD2 was altered in colony morphology and produced lower amounts of extracellular polysaccharide when compared with the wild-type strain.