title: rosR, a determinant of nodulation competitiveness in Rhizobium etli.
abstract: We previously described a Tn5 mutant of Rhizobium etli strain CE3, designated CE3003, that is decreased in nodulation competitiveness, reduced in competitive growth in the rhizosphere, and has a hydrophobic cell surface (R. S. Araujo, E. A. Robleto, and J. Handelsman, Appl. Environ. Microbiol., 60:1430-1436, 1994). To determine the molecular basis for the mutant phenotypes, we identified a 1.2-kb fragment of DNA derived from the parent that restored the wild-type phenotypes to the mutant. DNA sequence analysis indicated that this 1.2-kb fragment contained a single open reading frame that we designated rosR. The Tn5 insertion in CE3003 was within rosR. We constructed a derivative of CE3 that contained a deletion in rosR, and this mutant was phenotypically indistinguishable from CE3003 in cell surface and competitive characteristics. Based on the nucleotide sequence, the deduced RosR amino acid sequence is 80% identical to that of the Ros protein from Agrobacterium tumefaciens and the MucR protein from Rhizobium meliloti. Both Ros and MucR are transcriptional repressors that contain a putative zinc-finger DNA-binding domain. This study defines a gene, rosR, that is homologous to a family of transcriptional regulators and contributes to nodulation competitiveness of R. etli. Moreover, we established that a single gene affects nodulation competitiveness, competitive growth in the rhizosphere, and cell surface hydrophobicity.
authors.affiliation: Cellular and Molecular Biology Program, University of Wisconsin-Madison 53706, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Bittinger
authors.forename: J L
authors.initials: JL
authors.lastname: Milner
authors.forename: B J
authors.initials: BJ
authors.lastname: Saville
authors.forename: J
authors.initials: J
authors.lastname: Handelsman
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D007887:Fabaceae / Q000382:microbiology*; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010641:Phenotype; D010946:Plants, Medicinal; D012097:Repressor Proteins / Q000235:genetics*; D012231:Rhizobium / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D012097:Repressor Proteins