The interaction of CaM7 and CNGC14 regulates root hair growth in Arabidopsis

Oscillations in cytosolic free calcium determine the polarity of tip‐growing root hairs. The Ca2+ channel cyclic nucleotide gated channel 14 (CNGC14) contributes to the dynamic changes in Ca2+ concentration gradient at the root hair tip. However, the mechanisms that regulate CNGC14 are unknown. In this study, we detected a direct interaction between calmodulin 7 (CaM7) and CNGC14 through yeast two‐hybrid and bimolecular fluorescence complementation assays. We demonstrated that the third EF‐hand domain of CaM7 specifically interacts with the cytosolic C‐terminal domain of CNGC14. A two‐electrode voltage clamp assay showed that CaM7 completely inhibits CNGC14‐mediated Ca2+ influx, suggesting that CaM7 negatively regulates CNGC14‐mediated calcium signaling. Furthermore, CaM7 overexpressing lines phenocopy the short root hair phenotype of a cngc14 mutant and this phenotype is insensitive to changes in external Ca2+ concentrations. We, thus, identified CaM7‐CNGC14 as a novel interacting module that regulates polar growth in root hairs by controlling the tip‐focused Ca2+ signal. Calcium oscillations determine the polarity of tip‐growing root hairs. This study found that calcium sensor CaM7 (calmodulin 7) directly inhibits the calcium channel activity of CNGC14 (Ca2+ channel cyclic nucleotide gated channel) and works together as a novel interacting module to regulate polar growth in root hair.