Nuclear-associated Ca2+ oscillationsmediate plant responses to beneficial microbial partners-namely, nitrogen-fixing rhizobial bacteria that colonize roots of legumes and arbuscular mycorrhizal fungi that colonize roots of the majority of plant species. A potassium-permeable channel is known to be required for symbiotic Ca2+ oscillations, but the calcium channels themselves have been unknown until now. We show that three cyclic nucleotide-gated channels in Medicago truncatula are required for nuclear Ca2+ oscillations and subsequent symbiotic responses. These cyclic nucleotide-gated channels are located at the nuclear envelope and are permeable to Ca2+. We demonstrate that the cyclic nucleotide-gated channels form a complex with the postassium-permeable channel, which modulates nuclear Ca2+ release. These channels, like their counterparts in animal cells, might regulate multiple nuclear Ca2+ responses to developmental and environmental conditions.