Cloning and first functional characterization of a plant cyclic nucleotide-gated cation channel

Cyclic nucleotide-gated (cng) non-selective cation channels have been clone d from a number of animal systems. These channels;ire characterized by dire ct gating upon cAMP or cGMP binding to the intracellular portion of the cha nnel protein, which leads to an increase in channel conductance. Animal cng channels are involved in signal transduction systems; they translate stimu lus-induced changes in cytosolic cyclic nucleotide into altered cell membra ne potential and/or cation flux as part of a signal cascade pathway. Putati ve plant homologs of animal cng channels have been identified. However, fun ctional characterization (i.e. demonstration of cyclic-nucleotide-dependent ion currents) of a plant cng channel has not yet been accomplished. We rep ort the cloning and first functional characterization of a plant member of this family of ion channels. The Arabidopsis cDNA AtCNGC2 encodes a polypep tide with deduced homology to the alpha-subunit of animal channels, and fac ilitates cyclic nucleotide-dependent cation currents upon expression in a n umber of heterologous systems. AtCNGC2 expression in a yeast mutant lacking a low-affinity Kf uptake system complements growth inhibition only when li pophilic cyclic nucleotides are present in the culture medium. Voltage clam p analysis indicates that Xenopus laevis oocytes injected with AtCNGC2 cRNA demonstrate cyclic-nucleotide-dependent, inward-rectifying K+ currents. Hu man embryonic kidney cells (HEK293) transfected with AtCNGC2 cDNA demonstra te increased permeability to Ca2+ only in the presence of lipophilic cyclic nucleotides. The evidence presented here supports the functional classific ation of AtCNGC2 as a cyclic-nucleotide-gated cation channel, and presents the first direct evidence (to our knowledge) identifying a plant member of this ion channel family.