and Are Essential for Indeterminate Nodule Identity.

Symbiotic interactions between legume plants and rhizobia result in the formation of nitrogen-fixing nodules, but the molecular actors and the mechanisms allowing for the maintenance of nodule identity are poorly understood. (), (), and () are orthologs of Arabidopsis () and are members of the gene family, which has conserved roles in plant development and is essential for indeterminate and determinate nodule identity in legumes. The loss of function of , , and triggers a partial loss of nodule identity characterized by the development of ectopic roots arising from nodule vascular meristems. Here, we report the identification and characterization of a second gene involved in regulating indeterminate nodule identity in , is the paralog of and belongs to a second legume-specific subclade, the clade. expression was induced during early nodule formation, and it was expressed primarily in the nodule central meristem. mutants did not present any particular symbiotic phenotype; however, the loss of function of both and resulted in the complete loss of nodule identity and was accompanied by drastic changes in the expression of symbiotic, defense, and root apical meristem marker genes. double mutants developed only nonfixing root-like structures that were no longer able to host symbiotic rhizobia. This study provides original insights into the molecular basis underlying nodule identity in legumes forming indeterminate nodules.