Involved in symbiotic signaling. Required for root infection by symbiotic rhizobia, infection thread (IT) formation, and nodule development (PubMed:19074278). Probably not involved in nodule organogenesis (PubMed:19074278). Involved in arbuscular mycorrhizal (AM) symbiosis (PubMed:19074278). Required for fungal infection of the outer cortical cell layers, and for arbuscule development during the AM symbiosis, by binding, as a complex comprising CCaMK, CYCLOPS, and DELLA, to RAM1 promoter cis element thus promoting its expression (PubMed:19074278, PubMed:27020747). Acts downstream of CCAMK (PubMed:19074278). Binds to the promoter of ERN1 and strongly transactivates ERN1, a transcriptional regulator required for nodulation (PubMed:28503742). Forms homodimers. Interacts with CCAMK. Expressed in roots. Induced in nodules 21 days after rhizobial inoculation. Phosphorylated at the N-terminus by CCAMK. 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 (PubMed:19074278, PubMed:27020747). Stunted growth when grown in nitrogen-limiting conditions and in presence of Mesorhizobium loti (PubMed:19074278). Hairy roots of ipd3 mutant plants expressing a constitutively active form of CCAMK exhibit spontaneous nodule formation in the absence of rhizobia. Belongs to the CYCLOPS family.