Legumes symbioses: absence of Nod genes in photosynthetic bradyrhizobia.
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.
Giraud
Eric
E
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
Moulin
Lionel
L
Vallenet
David
D
Barbe
Valérie
V
Cytryn
Eddie
E
Avarre
Jean-Christophe
JC
Jaubert
Marianne
M
Simon
Damien
D
Cartieaux
Fabienne
F
Prin
Yves
Y
Bena
Gilles
G
Hannibal
Laure
L
Fardoux
Joel
J
Kojadinovic
Mila
M
Vuillet
Laurie
L
Lajus
Aurélie
A
Cruveiller
Stéphane
S
Rouy
Zoe
Z
Mangenot
Sophie
S
Segurens
Béatrice
B
Dossat
Carole
C
Franck
William L
WL
Chang
Woo-Suk
WS
Saunders
Elizabeth
E
Bruce
David
D
Richardson
Paul
P
Normand
Philippe
P
Dreyfus
Bernard
B
Pignol
David
D
Stacey
Gary
G
Emerich
David
D
Verméglio
André
A
Médigue
Claudine
C
Sadowsky
Michael
M
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
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