title: Legumes symbioses: absence of Nod genes in photosynthetic bradyrhizobia.
abstract: Leguminous plants (such as peas and soybeans) and rhizobial soil bacteria are symbiotic partners that communicate through molecular signaling pathways, resulting in the formation of nodules on legume roots and occasionally stems that house nitrogen-fixing bacteria. Nodule formation has been assumed to be exclusively initiated by the binding of bacterial, host-specific lipochito-oligosaccharidic Nod factors, encoded by the nodABC genes, to kinase-like receptors of the plant. Here we show by complete genome sequencing of two symbiotic, photosynthetic, Bradyrhizobium strains, BTAi1 and ORS278, that canonical nodABC genes and typical lipochito-oligosaccharidic Nod factors are not required for symbiosis in some legumes. Mutational analyses indicated that these unique rhizobia use an alternative pathway to initiate symbioses, where a purine derivative may play a key role in triggering nodule formation.
authors.affiliation: Institut de Recherche pour le Développement, Centre de Coopération International en Recherche Agronomique pour le Développement, Institut National de la Recherche Agronomique, Université Montpellier 2, France. giraud@mpl.ird.fr
authors.forename: Eric
authors.initials: E
authors.lastname: Giraud
authors.forename: Lionel
authors.initials: L
authors.lastname: Moulin
authors.forename: David
authors.initials: D
authors.lastname: Vallenet
authors.forename: Valérie
authors.initials: V
authors.lastname: Barbe
authors.forename: Eddie
authors.initials: E
authors.lastname: Cytryn
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Avarre
authors.forename: Marianne
authors.initials: M
authors.lastname: Jaubert
authors.forename: Damien
authors.initials: D
authors.lastname: Simon
authors.forename: Fabienne
authors.initials: F
authors.lastname: Cartieaux
authors.forename: Yves
authors.initials: Y
authors.lastname: Prin
authors.forename: Gilles
authors.initials: G
authors.lastname: Bena
authors.forename: Laure
authors.initials: L
authors.lastname: Hannibal
authors.forename: Joel
authors.initials: J
authors.lastname: Fardoux
authors.forename: Mila
authors.initials: M
authors.lastname: Kojadinovic
authors.forename: Laurie
authors.initials: L
authors.lastname: Vuillet
authors.forename: Aurélie
authors.initials: A
authors.lastname: Lajus
authors.forename: Stéphane
authors.initials: S
authors.lastname: Cruveiller
authors.forename: Zoe
authors.initials: Z
authors.lastname: Rouy
authors.forename: Sophie
authors.initials: S
authors.lastname: Mangenot
authors.forename: Béatrice
authors.initials: B
authors.lastname: Segurens
authors.forename: Carole
authors.initials: C
authors.lastname: Dossat
authors.forename: William L
authors.initials: WL
authors.lastname: Franck
authors.forename: Woo-Suk
authors.initials: WS
authors.lastname: Chang
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Saunders
authors.forename: David
authors.initials: D
authors.lastname: Bruce
authors.forename: Paul
authors.initials: P
authors.lastname: Richardson
authors.forename: Philippe
authors.initials: P
authors.lastname: Normand
authors.forename: Bernard
authors.initials: B
authors.lastname: Dreyfus
authors.forename: David
authors.initials: D
authors.lastname: Pignol
authors.forename: Gary
authors.initials: G
authors.lastname: Stacey
authors.forename: David
authors.initials: D
authors.lastname: Emerich
authors.forename: André
authors.initials: A
authors.lastname: Verméglio
authors.forename: Claudine
authors.initials: C
authors.lastname: Médigue
authors.forename: Michael
authors.initials: M
authors.lastname: Sadowsky
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism; D000581:Amidohydrolases / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D020369:Bradyrhizobium / Q000235:genetics* / Q000254:growth & development / Q000502:physiology*; D003583:Cytokinins / Q000378:metabolism; D007887:Fabaceae / Q000382:microbiology*; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D023281:Genomics; D008070:Lipopolysaccharides / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis; D018517:Plant Roots / Q000382:microbiology; D018547:Plant Stems / Q000382:microbiology*; D011687:Purines / Q000096:biosynthesis; D053204:Root Nodules, Plant / Q000382:microbiology / Q000502:physiology*; D015398:Signal Transduction; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D003583:Cytokinins; D008070:Lipopolysaccharides; D011687:Purines; C073606:nodB protein, Bacteria; D000217:Acyltransferases; C060770:NodA protein, Rhizobiales; D017351:N-Acetylglucosaminyltransferases; C060771:NodC protein, Rhizobiales; D000581:Amidohydrolases