text: Nod factors are potentially recognized by plant receptors made of two histidine kinases with extracellular LysM domain, which have been identified in L. japonicus, soybean, and M. truncatula . Binding of Nod factors to these receptors  depolarizes the plasma membrane of root hairs via an influx of Ca  which induce the expression of early nodulin (ENOD) genes and swelling of the root hairs. In M. truncatula, the signal transduction initiates by the activation of dmi1, dmi2, and dmi3 which lead to the deformation of root hairs, early nodulin expression, cortical cell division and bacterial infection. Additionally, nsp and hcl genes are recruited later and aid in the process of early nodulation expression, cortical cell division, and infection. Genes dmi1, dmi2, and dmi3  have also been found to aid in the establishment of interactions between M. truncatula and arbuscular mycorrhiza,  indicating that the two very different symbioses may share some common mechanisms. The end result is the nodule, the structure in which nitrogen is fixed.  Nod factors act by inducing changes in gene expression in the legume, most notable the nodulin genes, which are needed for nodule organogenesis.