Abstract: The invention includes a consensus nucleotide sequence found in the promoter regions of those Rhizobium and Bradyrhizobium nodulation genes which are activated by chemical inducer(s) in legume exudate. A promoter comprising the consensus sequence is a legume exudate-inducible promoter. A recombinant gene comprising a structural gene and a legume exudate-inducible promoter is selectively expressed in the presence of legume exudate or chemical inducer(s) and a functional nodD gene. The consensus nucleotide sequence isATCCAYNNYGYRGATGNWYKYKATCSAAWCAATCRATTTTACCARWYYKNSRR whereN is A, G, C or TY is C or TR is A or GW is A or TK is G or T andS is C or G.

Abstract: This invention provides useful promoters from the R. trifolii nifH gene for the construction of recombinant molecules to regulate foreign genes for expression under desired conditions. In particular, the promoters act to control expression of the foreign genes within root nodules formed by rhizobial bacterial strains in symbiotic combination with host plants.A rhizobium diagnostic segment (RDS) is also provided comprising a DNA segment found at more than one location in rhizobia, the RDS being species-specific, and detectable by DNA hybridization under stringent conditions. A recombinant plasmid comprising a RDS and a bacterial strain containing the plasmid are provided. Methods are provided for identifying species and strains of field isolates of Rhizobium, using RDS's. One RDS exemplified comprises 5' sequences from the R. trifolii nifH gene.

Abstract: A method of increasing nodulation of a plant capable of being nodulated by Bradyrhizobium sp. (Parasponis) is provided comprising infecting said plant with a Bradyrhizobium sp. (Parasponia) species mutated such that nodK is non-functional. One such method of mutation involves insertion upstream of nodABC constitutive promoter sequences capable of activating nodABC. The invention is exemplified by the inoculation of siratro with mutated Bradyrhizobium sp. (Parasponia) mutated by insertion of nptII promoter sequences in nodK upstream of nodABC so as to activate nodABC. As compared with inoculation with the corresponding wild-type Bradyrhizobium sp. (Parasponia), nodulation onset occurred five days earlier, nodulation number was doubled, and a 120% enhancement of plant yield was shown. Similar results were obtained regardless of the orientation of the nptII promoter-containing sequences within the nodK coding sequence.

Abstract: The nifH promoter regions of Bradyrhizobium japonicum and Bradyrhizobium sp. (parasponia) have been sequenced and found to be significantly homologous. Recombinant DNA molecules comprising foreign genes under the control of such promoters are provided. Rhizobial species containing such recombinant constructions, either in plasmids or integrated into the genome, are provided. These are especially useful for expressing desired foreign genes within root nodules.

Abstract: The nifD promoter regions of Bradyrhizobium japonicum and Bradyhizobium sp. (Parasponia) have been sequenced and found to be significantly homologous. Recombinant DNA molecules comprising foreign genes under the control of such promoters are provided. Rhizobial species containing such recombinant constructions, either in plasmids or integrated into the genome, are provided. These are especially useful for expressing desired foreign genes within root nodules.