Abstract: Mycorrhizal and rhizobial associations represent the two most important symbiotic relationships between higher plants and microorganisms, providing access to otherwise limiting supplies of phosphate and nitrogen, respectively. Although many higher plants are able to establish a symbiotic relationship with arbuscular mycorrhizal fungi, legumes are unusual among plants because they also form associations with nitrogen fixing soil bacteria called rhizobia. This symbiosis requires the production of bacterial signals, “Nod factors” that trigger several key developmental responses in the host plant (Dénarié et al., 1996). The DMI1 gene of the model legume M. truncatula plays a major role both in the early steps of Nod factor signaling and in the establishment of mycorrhizal symbiosis. Dmi1 mutants do not exhibit many of the early responses to Nod factors and are incapable of forming nitrogen fixing root nodules. Here we describe the cloning and preliminary characterization of DMI1.