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Early Symbiotic Responses Induced by Sinorhizobium meliloti ilvC Mutants in Alfalfa

January 2001 , Volume 14 , Number  1
Pages  55 - 62

Juan Carlos López , 1 Daniel H. Grasso , 1 Florian Frugier , 2 Martín D. Crespi , 2 and O. Mario Aguilar 1

1Instituto de Bioquímica y Biologia Molecular, Universidad Nacional de La Plata, Facultad de Ciencias Exactas, Calles 47 y 115, 1900-La Plata, Argentina; 2Institut des Sciences Végétales, Centre National de la Recherche Scientifique, F-91198 Gif-sur-Yvette Cedex, France

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Accepted 22 September 2000.

A mutation in the ilvC gene of Sinorhizobium meliloti 1021 determines a symbiotically defective phenotype. ilvC mutants obtained from different S. meliloti wild-type strains are able to induce root hair deformation on alfalfa roots and show variable activation of the common nodulation genes nodABC. All of these mutants are noninfective. The presence of extra copies of nodD3-syrM in an IlvC¯ background does not promote nod expression but allows the detection of low levels of Nod factor production. The sulphation of the Nod factor metabolites, however, is not affected. Furthermore, IlvC¯ strains induce a specific pattern of starch accumulation on alfalfa roots as well as of early nodulin expression. Hence, the pleiotropic action of the ilvC gene in S. meliloti may reveal novel complexities involved in the symbiotic interaction.

Additional keywords: isomeroreductase, plant response, symbiosis.

© 2001 The American Phytopathological Society