The invention relates to isolated DMI11 genes from Medicago truncatula which play a major role both in the early steps of Nod factor signaling that trigger several key developmental responses in the host plant and in the establishment of mycorrhizal symbiosis. The invention also relates to transgenic plants and plant cells expressing the DMI1 protein for increased root nodulation, and methods for transforming plants with a M. truncatula DMI1 gene.