High NaC l concentrations induce the nod genes of Rhizobium tropici C IAT899 in the absence of flavonoid inducers.

GUASCH B, ESTEVEZ J, DARDANELLI MS, SORIA-DÍAZ, M.E., FERNÁNDEZ DE CÓRDOBA, F., BALOG, C.I.A., GIL-SERRANO, A., THOMAS-OATES, J., HENSBERGEN, P.J., DEELDER, A.M., MEGÍAS, M. AND *VAN BRUSSEL, A.A.N.

MOLECULAR PLANT-MICROBE INTERACTIONS

AMER PHYTOPATHOLOGICAL SOC

Año: 2013 p. 451 - 460

0894-0282

The nod(ulation) genes of Rhizobium tropici CIAT899 can be induced by very low concentrations (nM ? µM 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(ulation) factors, which can induce root nodule primordia and pseudo-nodules 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 (Estévez et al., 2009). 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 radiolabelled glucosamine into newly synthesised Nod factors. This phenomenon was further investigated with thin layer plates, fusions of nod genes to the lacZ gene, HPLC, mass spectrometry and the formation of pseudo-nodules 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