title: Identification of Rhizobium plasmid sequences involved in recognition of Psophocarpus, Vigna, and other legumes.
abstract: Symbiotic DNA sequences involved in nodulation by Rhizobium must include genes responsible for recognizing homologous hosts. We sought these genes by mobilizing the symbiotic plasmid of a broad host-range Rhizobium MPIK3030 (= NGR234) that can nodulate Glycine max, Psophocarpus tetragonolobus, Vigna unguiculata, etc., into two Nod- Rhizobium mutants as well as into Agrobacterium tumefaciens. Subsequently, cosmid clones of pMPIK3030a were mobilized into Nod+ Rhizobium that cannot nodulate the chosen hosts. Nodule development was monitored by examining the ultrastructure of nodules formed by the transconjugants. pMPIK3030a could complement Nod- and Nif- deletions in R. leguminosarum and R. meliloti as well as enable A. tumefaciens to nodulate. Three non-overlapping sets of cosmids were found that conferred upon a slow-growing Rhizobium species, as well as on R. loti and R. meliloti, the ability to nodulate Psophocarpus and Vigna, thus pointing to the existence of three sets of host-specificity genes. Recipients harboring these hsn regions had truly broadened host-range since they could nodulate both their original hosts as well as MPIK3030 hosts.
mesh_terms: D001483:Base Sequence; D003001:Cloning, Molecular; D003433:Crosses, Genetic; D007887:Fabaceae / Q000235:genetics / Q000648:ultrastructure; D005838:Genotype; D008854:Microscopy, Electron; D010944:Plants / Q000235:genetics* / Q000648:ultrastructure; D010946:Plants, Medicinal; D010957:Plasmids; D012231:Rhizobium / Q000235:genetics* / Q000648:ultrastructure; D013045:Species Specificity; D013559:Symbiosis