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High NaCl Concentrations Induce the nod Genes of Rhizobium tropici CIAT899 in the Absence of Flavonoid Inducers

April 2013 , Volume 26 , Number  4
Pages  451 - 460

B. Guasch-Vidal,1 J. Estévez,2 M. S. Dardanelli,3 M. E. Soria-Díaz,4,5 F. Fernández de Córdoba,4 C. I. A. Balog,6 H. Manyani,2 A. Gil-Serrano,4 J. Thomas-Oates,7 P. J. Hensbergen,6 A. M. Deelder,6 M. Megías,2 and A. A. N. van Brussel8

1Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain; 2Departamento de Microbiología y Parasitología, Facultad de Farmacia, Universidad de Sevilla; 3Departamento de Biología Molecular, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto. Río Cuarto, Argentina; 4Departamento de Química Orgánica, Facultad de Química, Universidad de Sevilla; 5Servicio de Espectrometría de Masas, Centro de investigación, tecnología e innovación (CITIUS), Universidad de Sevilla; 6Biomolecular Mass Spectrometry Unit, Department of Parasitology, Leiden University Medical Center (LUMC), Leiden, The Netherlands; 7Department of Chemistry, University of York, Heslington, York, U.K.; 8Sylvius Laboratory, Institute of Biology, Leiden University. Leiden, The Netherlands

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Accepted 20 November 2012.

The nodulation (nod) genes of Rhizobium tropici CIAT899 can be induced by very low concentrations (micromolar to nanomolar range) of several flavonoid molecules secreted by the roots of leguminous plants under a number of different conditions. Some of these conditions have been investigated and appear to have a great influence on the concentration and the number of different Nod factors, which can induce root nodule primordia and pseudonodules in several leguminous plant roots. In one such condition, we added up to 300 mM NaCl to the induction medium of R. tropici CIAT899 containing the nod gene inducer apigenin. At the higher concentrations of NaCl, larger amounts and more different Nod factors were produced than in the absence of extra NaCl. To our surprise, under control conditions (300 mM NaCl without apigenin), some Nod-factor-like spots were also observed on the thin-layer plates used to detect incorporation of radiolabeled glucosamine into newly synthesized Nod factors. This phenomenon was further investigated with thin-layer plates, fusions of nod genes to the lacZ gene, high-performance liquid chromatography, mass spectrometry, and the formation of pseudonodules on bean roots. Here, we report that, in the absence of flavonoid inducers, high concentrations of NaCl induced nod genes and the production of Nod factors.

© 2013 The American Phytopathological Society