title: The twin-arginine translocation (Tat) system is essential for Rhizobium-legume symbiosis.
abstract: The Tat (twin-arginine translocation) system mediates export of periplasmic proteins in folded conformation. Proteins transported via Tat contain a characteristic twin-arginine motif in their signal peptide. Genetic determinants (tatABC genes) of the Tat system from Rhizobium leguminosarum bv. viciae were cloned and characterized, and a tatBC deletion mutant was constructed. The mutant lacked the ability for membrane targeting of hydrogenase, a known Tat substrate, and was impaired in hydrogenase activity. Interestingly, in the absence of a functional Tat system, only small, white nodules unable to fix nitrogen were induced in symbiosis with pea plants. Analysis of nodule structure and location of green fluorescent protein (GFP)-tagged bacteria within nodules indicated that the symbiotic process was blocked in the tat mutant at a stage previous to bacteria release into cortical cells. The R. leguminosarum Tat-deficient mutant lacked a functional cytochrome bc1 complex. This was consistent with the fact that R. leguminosarum Rieske protein, a key component of the symbiosis-essential cytochrome bc1 complex, contained a typical twin-arginine signal peptide. However, comparative analyses of nodule structure indicated that nodule development in the tat mutant was arrested at an earlier step than in a cytochrome bc1 mutant. These data indicate that the Tat pathway is also critical for proteins relevant to the initial stages of the symbiotic process.
authors.affiliation: Laboratorio de Microbiología, Departamento de Biotecnología, Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Politécnica de Madrid, Spain.
authors.forename: Stefania
authors.initials: S
authors.lastname: Meloni
authors.forename: Luis
authors.initials: L
authors.lastname: Rey
authors.forename: Stephan
authors.initials: S
authors.lastname: Sidler
authors.forename: Juan
authors.initials: J
authors.lastname: Imperial
authors.forename: Tomás
authors.initials: T
authors.lastname: Ruiz-Argüeso
authors.forename: José M
authors.initials: JM
authors.lastname: Palacios
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry; D045304:Cytochromes c / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006864:Hydrogenase / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D009586:Nitrogen Fixation; D018532:Pisum sativum / Q000382:microbiology*; D016961:Rhizobium leguminosarum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; C408585:twin-arginine translocase complex, E coli; D045304:Cytochromes c; D006864:Hydrogenase