Identification of Cyclic GMP-Activated Nonselective Ca2+-Permeable Cation Channels and Associated CNGC5 and CNGC6 Genes in Arabidopsis Guard Cells    

Abstract

Cytosolic Ca2+ in guard cells plays an important role in stomatal movement responses to environmental stimuli. These cytosolic Ca 2+ increases result from Ca 2+ influx through Ca 2+ -permeable channels in the plasma membrane and Ca 2+ release from intracellular organelles in guard cells. However, the genes encoding defined plasma membrane Ca 2+ -permeable channel activity remain unknown in guard cells and, with some exceptions, largely unknown in higher plant cells. Here, we report the identification of two Arabidopsis (Arabidopsis thaliana) cation channel genes, CNGC5 and CNGC6, that are highly expressed in guard cells. Cytosolic application of cyclic GMP (cGMP) and extracellularly applied membrane-permeable 8-Bromoguanosine 39,59-cyclic monophosphate-cGMP both activated hyperpolarization-induced inward-conducting currents in wild-type guard cells using Mg 2+ as the main charge carrier. The cGMP-activated currents were strongly blocked by lanthanum and gadolinium and also conducted Ba 2+ , Ca 2+, and Na + ions. cngc5 cngc6 double mutant guard cells exhibited dramatically impaired cGMP-activated currents. In contrast, mutations in CNGC1, CNGC2, and CNGC20 did not disrupt these cGMP-activated currents. The yellow fluorescent protein-CNGC5 and yellow fluorescent protein-CNGC6 proteins localize in the cell periphery. Cyclic AMP activated modest inward currents in both wild-type and cngc5cngc6 mutant guard cells. Moreover, cngc5 cngc6 double mutant guard cells exhibited functional abscisic acid (ABA)-activated hyperpolarization-dependent Ca 2+ -permeable cation channel currents, intact ABA-induced stomatal closing responses, and whole-plant stomatal conductance responses to darkness and changes in CO 2 concentration. Furthermore, cGMPactivated currents remained intact in the growth controlled by abscisic acid2 and abscisic acid insensitive1 mutants. This research demonstrates that the CNGC5 and CNGC6 genes encode unique cGMP-activated nonselective Ca 2+ -permeable cation channels in the plasma membrane of Arabidopsis guard cells.Plants lose water via transpiration and take in CO 2 for photosynthesis through stomatal pores. Each stomatal pore is surrounded by two guard cells, and stomatal movements are driven by the change of turgor pressure in guard cells. The intracellular second messenger Ca 2+ functions in guard cell signal transduction (Schroeder and

Tip‐localized Ca2+‐permeable channels control pollen tube growth via kinase‐dependent R‐ and S‐type anion channel regulation

“…Current–voltage characteristics of CNGC18 in HEK293T cells (Gao et al ., ) are very similar to features of Ca 2+ ‐permeable channels in guard cells (Pei et al ., ; Wang et al ., ), root hair tips (Very & Davies, ), or PT tip protoplasts (Shang et al ., ; Qu et al ., ; Wu et al ., ). Recent genetic evidence points to CNGCs as prime candidates for pollen Ca 2+ ‐permeable channels in general and CNGC18 in particular (Wang et al ., ; Gao et al ., , ). Employing the combination of the TEVC technique and imaging would shed light on the contribution of the aforementioned GLRs and CNGCs to shape the apical Ca 2+ gradient.…”

Calcium transport across plant membranes: mechanisms and functions

“…Wang et al . () found that CNGC5 and CNGC6 of A. thaliana guard cell PM are ABA‐insensitive, cGMP‐dependent Ca 2+ ‐permeable channels.…”

Cyclic nucleotide gated channel 10 negatively regulates salt tolerance by mediating Na+ transport in Arabidopsis

“…The CNGC5 and CNGC6 are required for cyclic GMP (cGMP)-activated nonselective Ca 2+ -permeable cation channel activity in the plasma membrane of A. thaliana guard cells and suggest CNGC5 and CNGC6 may also regulate Ca 2+ influx and Ca 2+ signaling (Finka et al 2012;Wang et al 2013). CNGC18 is expressed specifically in pollen and is required for polarized growth of pollen (Frietsch et al 2007).…”