Involved symbiotic signaling. Required for root infection by symbiotic rhizobia, infection thread (IT) formation, and nodule development. Required for proper induction of early nodulin gene expression. Probably not involved in nodule organogenesis. Involved in arbuscular mycorrhizal (AM) symbiosis. Required for fungal infection of the outer cortical cell layers, and for arbuscule development during the AM symbiosis. Acts downstream of CCAMK (PubMed:21692638). Required for symbiosome formation (i.e. the release of the bacteria from the ITs) and subsequent symbiosome development. Required for the expression of the nodule-specific RPG gene, which controls proper IT growth and is essential for symbiosome formation (PubMed:21787150). Acts upstream of ERN1, a transcriptional regulator required for nodulation (PubMed:17449807). Forms homodimers. Interacts with CCAMK. Highly expressed in roots. Expressed in root hairs and nodules. Not detected in leaves or flowers. No visible phenotype under normal growth conditions, but roots of mutant plants are impaired in the interaction with both rhizobia and the arbuscular mycorrhiza (AM) fungus Glomus intraradices. Stunted growth when grown in nitrogen-limiting conditions and in presence of Sinorhizobium meliloti. Belongs to the CYCLOPS family.