Molecular Cloning and Functional Analysis of a Na(+)-Insensitive K(+) Transporter of Capsicum chinense Jacq

High-affinity K(+) (HAK) transporters are encoded by a large family of genes and are ubiquitous in the plant kingdom. These HAK-type transporters participate in low- and high-affinity potassium (K(+)) uptake and are crucial for the maintenance of K(+) homeostasis under hostile conditions. In this study, the full-length cDNA of CcHAK1 gene was isolated from roots of the habanero pepper (Capsicum chinense). CcHAK1 expression was positively regulated by K(+) starvation in roots and was not inhibited in the presence of NaCl. Phylogenetic analysis placed the CcHAK1 transporter in group I of the HAK K(+) transporters, showing that it is closely related to Capsicum annuum CaHAK1 and Solanum lycopersicum LeHAK5. Characterization of the protein in a yeast mutant deficient in high-affinity K(+) uptake (WΔ3) suggested that CcHAK1 function is associated with high-affinity K(+) uptake, with K(m) and V(max) for Rb of 50 μM and 0.52 nmol mg(−1) min(−1), respectively. K(+) uptake in yeast expressing the CcHAK1 transporter was inhibited by millimolar concentrations of the cations ammonium ([Formula: see text]) and cesium (Cs(+)) but not by sodium (Na(+)). The results presented in this study suggest that the CcHAK1 transporter may contribute to the maintenance of K(+) homeostasis in root cells in C. chinense plants undergoing K(+)-deficiency and salt stress.