Fig. 9: CPK1-mediated phosphorylation of CNGC5/6/9 is necessary and sufficient to retain a sharp cytosolic Ca2+ gradient at the apex of elongating RHs.
The cytosolic Ca2+ gradient at the tips of growing RH was monitored by measuring the FRET/CFP ratio of YC3.6 in the Arabidopsis lines expressing the calcium sensor YC3.6. A sharp cytosolic Ca2+ gradient was observed in wild-type RHs, but this was dramatically attenuated in the cpk1-1, shrh1, and cpk1 shrh1 mutants. The sharp cytosolic Ca2+ gradient was successfully restored to wild-type-like levels in the RHs of cpk1-1 and shrh1 by the expression of aCNGCs, but not by the expression of the iCNGCs, under their respective native promoters. a Pseudo images of typical YC3.6 FRET/CFP ratios in RHs of wild-type, cpk1-1, shrh1, and cpk1 shrh1 mutants, and the CNGC5S20A(shrh1), CNGC5S20D(shrh1), CNGC6S27A(shrh1), CNGC6S27D(shrh1), CNGC9S26A(shrh1), CNGC9S26D(shrh1), CNGC5S20A(cpk1-1), CNGC5S20D(cpk1-1), CNGC6S27A(cpk1-1), CNGC6S27D(cpk1-1), CNGC9S26D(cpk1-1), and CNGC9S26A(cpk1-1) transgenic lines. b YC3.6 FRET/CFP ratios reflecting cytosolic Ca2+ gradients at RH apices. Scale bars, 10 μm in (a). n = 24, 20, 25, 25, 16, 25, 11, 23, 24, 24, 12, 24, 18, 18, 19, and 23 biologically independent RHs for the lines as shown from left to right in (b). The data are presented as means ± SEM, and samples with different letters are significantly different with P < 0.05 (one-way ANOVA) in (b). Source data are provided as a Source Data file.
