Sequence and analysis of the nodABC region of Rhizobium fredii USDA257, a nitrogen-fixing symbiont of soybean and other legumes.
We cloned and analyzed nodABC from Rhizobium fredii USDA257. These genes are thought to have common functions in initiation of nitrogen-fixing nodules by all rhizobia. In USDA257, they were located in a 9.2-kb EcoRI fragment that was not closely linked to either of two copies of the regulatory gene, nodD. nodABC was present in a 3,094-base pair (bp) sequenced region, which also included a consensus nod-box promoter. The three open reading frames contained 654, 642, and 1,239 bp, respectively, and encoded deduced proteins of 21.9, 23.4, and 44.7 kD. The sequence of the nodABC region of USDA257 was generally homologous with corresponding regions from other rhizobia, but it diverged significantly in the 5' non-translated region and in the 3'terminus of nodC. nodC was not translationally coupled to nodSU, as in another soybean symbiont, Bradyrhizobium japonicum, and the deduced NodC protein was the shortest of any such proteins yet described. Site-directed mutagenesis of the 9.2-kb EcoRI fragment confirmed that nodA, nodB, and nodC are essential for nodulation of soybean, but failed to identify other linked nod genes. Daidzein, a major isoflavone from soybean roots, was the most potent of nine tested flavonoids in activating a plasmid-borne nodC::lacZ fusion. The 9.2-kb fragment complemented nodA-, nodB-, and nodC- mutants of R. meliloti to the Nod+ phenotype on Medicago sativa, M. truncatula, and Trigonella foenum-graecum. Nodule numbers, percentage of nodulated plants, and shoot dry weights, however, were considerably less than in plants inoculated with mutants complemented with nodABC from R. meliloti.
Krishnan
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HB
Department of Plant Pathology, University of Missouri, Columbia 65211.
Pueppke
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SG
D000217:Acyltransferases; D000581:Amidohydrolases; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D003854:Deoxyribonucleotides; D007887:Fabaceae / Q000382:microbiology*; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D017351:N-Acetylglucosaminyltransferases; D009586:Nitrogen Fixation / Q000235:genetics*; D009876:Operon; D010946:Plants, Medicinal; D010957:Plasmids; D012231:Rhizobium / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D013025:Glycine max / Q000382:microbiology*; D013045:Species Specificity; D013559:Symbiosis
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D003854:Deoxyribonucleotides; C073606:nodB protein, Bacteria; D000217:Acyltransferases; C060770:NodA protein, Rhizobiales; D017351:N-Acetylglucosaminyltransferases; C060771:NodC protein, Rhizobiales; D000581:Amidohydrolases