The DMI1 Gene Encodes A Protein That Is Required For The Early Steps Of Bacterial And Fungal Symbioses

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 (Dnari 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. The DMI1 gene encodes a novel protein with low global similarity to ligand-gated cation channels of archaea. The protein is highly conserved in angiosperms and ancestral to land plants. Interestingly a putative A. thaliana DMI1 orthologous gene is expressed in roots. As A. thaliana is unable to establish a mycorrhizal symbiosis, this finding suggests that DMI1 may also exhibit a function that is independent of symbiotic interactions.