Arabidopsis thaliana CYCLIC NUCLEOTIDE‐GATED CHANNEL2 mediates extracellular ATP signal transduction in root epidermis

Damage can be signalled by extracellular ATP (eATP) using plasma membrane (PM) receptors to effect cytosolic free calcium ion ([Ca(2+)](cyt)) increase as a second messenger. The downstream PM Ca(2+) channels remain enigmatic. Here, the Arabidopsis thaliana Ca(2+) channel subunit CYCLIC NUCLEOTIDE‐GATED CHANNEL2 (CNGC2) was identified as a critical component linking eATP receptors to downstream [Ca(2+)](cyt) signalling in roots. Extracellular ATP‐induced changes in single epidermal cell PM voltage and conductance were measured electrophysiologically, changes in root [Ca(2+)](cyt) were measured with aequorin, and root transcriptional changes were determined by quantitative real‐time PCR. Two cngc2 loss‐of‐function mutants were used: cngc2‐3 and defence not death1 (which expresses cytosolic aequorin). Extracellular ATP‐induced transient depolarization of Arabidopsis root elongation zone epidermal PM voltage was Ca(2+) dependent, requiring CNGC2 but not CNGC4 (its channel co‐subunit in immunity signalling). Activation of PM Ca(2+) influx currents also required CNGC2. The eATP‐induced [Ca(2+)](cyt) increase and transcriptional response in cngc2 roots were significantly impaired. CYCLIC NUCLEOTIDE‐GATED CHANNEL2 is required for eATP‐induced epidermal Ca(2+) influx, causing depolarization leading to [Ca(2+)](cyt) increase and damage‐related transcriptional response.