Use of a Subtractive Hybridization Approach to Identify New Medicago truncatula Genes Induced During Root Nodule Development. Pascal Gamas. Laboratoire de Biologie Moleculaire des Relations Plantes-Microorganismes, INRA-CNRS, BP 27, 31326 Castanet-Tolosan Cedex, France. Fernanda de Carvalho Niebel, Nicole Lescure, and Julie V. Cullimore Laboratoire de Biologie Moleculaire des Relations Plantes-Microorganismes, INRA-CNRS, BP 27, 31326 Castanet-Tolosan Cedex, France. MPMI 9:233-242. Accepted 16 February 1996. Copyright 1996 The American Phytopathological Society.

We report the identification of new molecular markers associated with different stages of Rhizobium-induced nodule development in the legume Medicago truncatula. A cDNA library was constructed from pre-nitrogen-fixing M. truncatula nodules, and differentially screened with a polymerase chain reaction-amplified subtracted probe. Twenty-nine new families of nodulin cDNA clones, designated MtNl to MtN29, were thus identified in addition to clones for several known nodulins. All MtN genes were shown by Northern (RNA) hybridization analysis to be induced during nodulation, some of them well before nodule emergence. The MtN genes were classified into three groups depending on their expression kinetics. The expression of three MtN genes showed a limited induction by Nod factors purified from Rhizobium meliloti. Ho-mologies with a variety of proteins were found for the deduced amino acid sequences of 10 of the MtN genes.