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Genetic and Cytogenetic Mapping of DMI1, DMI2, and DMI3 Genes of Medicago truncatula Involved in Nod Factor Transduction, Nodulation, and Mycorrhization

November 2002 , Volume 15 , Number  11
Pages  1,108 - 1,118

Jean-Michel Ané , 1 Julien Lévy , 1 Philippe Thoquet , 1 Olga Kulikova , 2 Françoise de Billy , 1 Varma Penmetsa , 3 Dong-Jin Kim , 3 Frédéric Debellé , 1 Charles Rosenberg , 1 Douglas R. Cook , 3 Ton Bisseling , 2 Thierry Huguet , 1 and Jean Dénarié 1

1Laboratoire de Biologie Moléculaire des Relations Plante-Microorganismes, CNRS-INRA UMR215, BP27, 31326 Castanet-Tolosan Cedex, France; 2Laboratory of Molecular Biology, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands; 3Department of Plant Pathology, University of California, Davis CA95616, U.S.A.

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Accepted 11 July 2002.

The DMI1, DMI2, and DMI3 genes of Medicago truncatula, which are required for both nodulation and mycorrhization, control early steps of Nod factor signal transduction. Here, we have used diverse approaches to pave the way for the map-based cloning of these genes. Molecular amplification fragment length polymorphism markers linked to the three genes were identified by bulked segregant analysis. Integration of these markers into the general genetic map of M. truncatula revealed that DMI1, DMI2, and DMI3 are located on linkage groups 2, 5, and 8, respectively. Cytogenetic studies using fluorescent in situ hybridization (FISH) on mitotic and pachytene chromosomes confirmed the location of DMI1, DMI2, and DMI3 on chromosomes 2, 5, and 8. FISH-pachytene studies revealed that the three genes are in euchromatic regions of the genome, with a ratio of genetic to cytogenetic distances between 0.8 and 1.6 cM per μm in the DMI1, DMI2, and DMI3 regions. Through grafting experiments, we showed that the genetic control of the dmi1, dmi2, and dmi3 nodulation phenotypes is determined at the root level. This means that mutants can be transformed by Agrobacterium rhizogenes to accelerate the complementation step of map-based cloning projects for DMI1, DMI2, and DMI3.

© 2002 The American Phytopathological Society