The cyclic nucleotide-gated channels AtCNGC11 and 12 are involved in multiple Ca(2+)-dependent physiological responses and act in a synergistic manner

Arabidopsis cyclic nucleotide-gated ion channels (AtCNGCs) form a large family consisting of 20 members. These channels have so far been reported to be involved in a diverse range of physiological phenomena. For example, AtCNGC18 was reported to play an important role in pollen tube growth, while AtCNGC2, 4, 11, and 12 were implicated in mediating pathogen defence. To identify additional functions for AtCNGC11 and 12, various physiological aspects were analysed using both AtCNGC11 and 12 single knockout mutants as well as a double mutant. Although AtCNGC11 and 12 can function as K(+) and Ca(2+) channels in yeast, it was found that the loss of AtCNGC11 and 12 in Arabidopsis caused increased sensitivity to Ca(2+) but not K(+), indicating a specific function for these genes in Ca(2+) signalling in planta. However, they did not show an alteration in Ca(2+) accumulation, suggesting that AtCNGC11 and 12 are not involved in general Ca(2+) homeostasis but rather in the endogenous movement of Ca(2+) and/or Ca(2+) signalling. Furthermore, these channels synergistically contribute to the generation of a Ca(2+) signal that leads to gravitropic bending. Finally, AtCNGC11 and 12 gene expression was induced during dark-induced senescence and AtCNGC11 and 12 knockout mutants displayed enhanced chlorophyll loss, which was even more pronounced in the double mutant, also indicating synergistic roles in senescence. The findings indicate that (i) some CNGC family members have multiple physiological functions and (ii) some plant CNGCs share the same biological function and work in a synergistic manner.