title: Homoserine catabolism by Rhizobium leguminosarum bv. viciae 3841 requires a plasmid-borne gene cluster that also affects competitiveness for nodulation.
abstract: Homoserine represents a substantial component of pea root exudate that may be important for plant-microbe interactions in the rhizosphere. We identified a gene cluster on plasmid pRL8JI that is required for homoserine utilization by Rhizobium leguminosarum bv. viciae. The genes are arranged as two divergently expressed predicted operons that were induced by L-homoserine, pea root exudate, and were expressed on pea roots. A mutation in gene pRL80083 that prevented utilization of homoserine as a sole carbon and energy source affected the mutant's ability to nodulate peas and lentils competitively. The homoserine gene cluster was present in approximately 47% of natural R. leguminosarum isolates (n = 59) and was strongly correlated with homoserine utilization. Conjugation of pRL8JI to R. leguminosarum 4292 or Agrobacterium tumefaciens UBAPF2 was sufficient for homoserine utilization. The presence of L-homoserine increased conjugation efficiency of pRL8JI from R. leguminosarum to a pRL8JI-cured derivative of R. leguminosarum 1062 and to A. tumefaciens UBAPF2, and induced expression of the plasmid transfer gene trbB; however, there was no difference in conjugation efficiency or trbB expression with A. tumefaciens UBAPF2pRL8-Gm as the donor suggesting that other genes in R. leguminosarum may contribute to regulating conjugation of pRL8 in the presence of homoserine.
authors.affiliation: Biology Department, University of Regina, Regina, SK, S4S0A2, Canada.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Vanderlinde
authors.forename: Michael F
authors.initials: MF
authors.lastname: Hynes
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Yost
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006714:Homoserine / Q000378:metabolism*; D005810:Multigene Family; D009154:Mutation; D009876:Operon; D018532:Pisum sativum / Q000382:microbiology*; D010957:Plasmids / Q000235:genetics* / Q000378:metabolism; D016961:Rhizobium leguminosarum / Q000235:genetics / Q000378:metabolism*; D053204:Root Nodules, Plant / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins; D006714:Homoserine