June
2010
, Volume
23
, Number
6
Pages
760
-
770
Authors
Katia Bonaldi,1,2
Benjamin Gourion,1
Joel Fardoux,1
Laure Hannibal,1
Fabienne Cartieaux,1
Marc Boursot,1
David Vallenet,3
Clémence Chaintreuil,1
Yves Prin,4
Nico Nouwen,1 and
Eric Giraud1
Affiliations
1Laboratoire des Symbioses Tropicales et Méditerranéennes, IRD, UMR-IRD/SupAgro/INRA/UM2/CIRAD, F-34398 Montpellier, France; 2UM2, F-34398 Montpellier, France; 3Genoscope, CNRS-UMR 8030, Atelier de Génomique Comparative, F-91057 Evry, France; 4Laboratoire des Symbioses Tropicales et Méditerranéennes, CIRAD, UMR-IRD/SupAgro/INRA/UM2/CIRAD, F-34398 Montpellier, France
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RelatedArticle
Accepted 23 February 2010.
Abstract
Photosynthetic Bradyrhizobium strains possess the unusual ability to form nitrogen-fixing nodules on a specific group of legumes in the absence of Nod factors. To obtain insight into the bacterial genes involved in this Nod-independent symbiosis, we screened 15,648 Tn5 mutants of Bradyrhizobium sp. strain ORS278 for clones affected in root symbiosis with Aeschynomene indica. From the 268 isolated mutants, 120 mutants were altered in nodule development (Ndv--) and 148 mutants were found to be deficient in nitrogen fixation (Fix--). More than 50% of the Ndv-- mutants were found to be altered in purine biosynthesis, strengthening the previous hypothesis of a symbiotic role of a bacterial purine derivative during the Nod-independent symbiosis. The other Ndv-- mutants were auxotrophic for pyrimidines and amino acids (leucine, glutamate, and lysine) or impaired in genes encoding proteins of unknown function. The Fix-- mutants were found to be affected in a wide variety of cellular processes, including both novel (n = 56) and previously identified (n = 31) genes important in symbiosis. Among the novel genes identified, several were involved in the Calvin cycle, suggesting that CO2 fixation could play an important role during this symbiosis.
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© 2010 The American Phytopathological Society