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 ([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. Extracellular ATP-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 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 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. CYCLIC NUCLEOTIDE-GATED CHANNEL2 is required for eATP-induced epidermal Ca2+ influx, causing depolarization leading to [Ca2+ ]cyt increase and damage-related transcriptional response.

Differences between seedlings and flowers in anti-ROS based heat responses of Arabidopsis plants deficient in cyclic nucleotide gated channel 2.

Cyclic nucleotide gated channel 2 (CNGC2) in Arabidopsis has been identified as one of the putative heat sensors which might play a key role in the regulation of heat acclimation. However, it is still not understood how CNGC2 controls heat stress responses during different growth stages. This study aimed to characterize the differences in heat stress responses between seedlings and flowers of Arabidopsis plants deficient in CNGC2. Seedlings of Arabidopsis plants deficient in CNGC2 showed enhanced tolerance to heat stress accompanied by higher accumulation of heat response proteins such as multiprotein bridging factor 1c (MBF1c), ascorbate peroxidases (APXs) and heat shock proteins (HSPs). On the other hand, seed production of these knockout lines was more sensitive to heat stress. In contrast to seedlings, accumulation of MBF1c and APX proteins in flowers of these knockout lines was lower than or almost comparable with that in WT plants under heat stress. In addition, plants deficient in CNGC2 showed dramatically higher accumulation of H2O2 in flowers, but, only slightly higher accumulation in seedlings compared with WT plants. These results suggest that the stage-dependent differences in heat stress response of Arabidopsis regulated by CNGC2 might rely on regulatory mechanisms of APX1-and MBF1c-dependent pathways and H2O2 homeostasis.