Arabidopsis thaliana Cyclic Nucleotide-Gated Channel2 mediates extracellular ATP signal transduction in root epidermis.

Abstract

Damage can be signalled by extracellular ATP (eATP) using plasma membrane (PM) receptors to effect cytosolic free Ca2+ ([Ca2+ ]cyt ) increase as a second messenger. The downstream PM Ca2+ channels remain enigmatic. Here, the Arabidopsis thaliana Ca2+ channel subunit Cyclic Nucleotide-Gated Channel2 (CNGC2) was identified as a critical component linking eATP receptors to downstream [Ca2+ ]cyt signalling in roots. eATP-induced changes in single epidermal cell PM voltage and conductance were measured electrophysiologically, changes in root [Ca2+ ]cyt were measured with aequorin and root transcriptional changes were determined by qRT-PCR. Two cngc2 loss of function mutants were used: cngc2-3 and dnd1 (which expresses cytosolic aequorin). eATP-induced transient depolarisation of Arabidopsis root elongation zone epidermal PM voltage was Ca2+ -dependent, requiring CNGC2 but not CNGC4 (its channel co-subunit in immunity signalling). Activation of PM Ca2+ influx currents also required CNGC2. The eATP-induced [Ca2+ ]cyt increase and transcriptional response in cngc2 roots were significantly impaired. CNGC2 is required for eATP-induced epidermal Ca2+ influx, causing depolarisation leading to [Ca2+ ]cyt increase and damage-related transcriptional response.