Three CNGC Family Members, CNGC5, CNGC6, and CNGC9, Are Required for Constitutive Growth of Root Hairs as Ca-Permeable Channels.

The genetic identities of Ca channels in root hair (RH) tips essential for constitutive RH growth have remained elusive for decades. Here, we report the identification and characterization of three cyclic nucleotide-gated channel (CNGC) family members, CNGC5, CNGC6, and CNGC9, as Ca channels essential for constitutive RH growth in . We found that the triple mutant (designated ) showed significantly shorter and branching RH phenotypes as compared with the wild type. The defective RH growth phenotype of could be rescued by either the expression of , , or single gene or by the supply of high external Ca, but could not be rescued by external K supply. Cytosolic Ca imaging and patch-clamp data in HEK293T cells showed that these three CNGCs all function as Ca-permeable channels. Cytosolic Ca imaging in growing RHs further showed that the Ca gradients and their oscillation in RH tips were dramatically attenuated in compared with those in the wild type. Phenotypic analysis revealed that these three CNGCs are Ca channels essential for constitutive RH growth, with different roles in RHs from the conditional player CNGC14. Moreover, we found that these three CNGCs are involved in auxin signaling in RHs. Taken together, our study identified CNGC5, CNGC6, and CNGC9 as three key Ca channels essential for constitutive RH growth and auxin signaling in .