CPK1 activates CNGCs through phosphorylation for Ca2+ signaling to promote root hair growth in Arabidopsis
Zhu Mei-Jun, Boya Du, Yan-Qiu Tan, Yang Yang, Yang Zhang, Yong‐Fei Wang
Abstract
Abstract Cyclic nucleotide-gated channel 5 (CNGC5), CNGC6, and CNGC9 (CNGC5/6/9 for simplicity) control Arabidopsis root hair (RH) growth by mediating the influx of external Ca 2+ to establish and maintain a sharp cytosolic Ca 2+ gradient at RH tips. However, the underlying mechanisms for the regulation of CNGCs remain unknown. We report here that calcium dependent protein kinase 1 (CPK1) directly activates CNGC5/6/9 to promote Arabidopsis RH growth. The loss-of-function mutants cpk1-1 , cpk1-2 , cngc5-1 cngc6-2 cngc9-1 ( shrh1 / short root hair 1 ), and cpk1 shrh1 show similar RH phenotypes, including shorter RHs, more RH branching, and dramatically attenuated cytosolic Ca 2+ gradients at RH tips. The main CPK1-target sites are identified as Ser20, Ser27, and Ser26 for CNGC5/6/9, respectively, and the corresponding alanine substitution mutants fail to rescue RH growth in shrh1 and cpk1-1 , while phospho-mimic versions restore the cytosolic Ca 2+ gradient at RH apex and rescue the RH phenotypes in the same Arabidopsis mutants. Thus we discover the CPK1-CNGC modules essential for the Ca 2+ signaling regulation and RH growth in Arabidopsis.