Cakc2.1 , an Ortholog of the Arabidopsis K + Channel KAT1 , Positively Mediates Pepper Fruit Coloration

ABSTRACT Potassium (K + ), the most abundant cellular cation, plays essential roles in various plant biological functions, such as stomatal movement and stress responses. Although the molecular mechanisms of K + uptake and transport have been established in the model plant Arabidopsis thaliana , in addition to other plant species such as rice and grape, little is known about these mechanisms in pepper. In this study, CaKC2.1 was cloned from pepper ( Capsicum annuum L . ), which encodes a putative plant voltage‐gated K + channel protein. CaKC2.1 shares 61% amino acid sequence identity with Arabidopsis AtKAT1, a group II plant voltage‐gated K + channel localized to the plasma membrane. The highest expression level of CaKC2.1 was in mature pepper fruits (red), and the expression in roots and immature fruits (green) was very low. The heterologous expression of CaKC2.1 in the K + uptake‐deficient yeast mutant CY162 ( trk1Δtrk2Δ ) rescued the lethal phenotype of the strain grown on low‐K + medium, suggesting the capability of CaKC2.1 in K + uptake and transport. The overexpression of CaKC2.1 in Arabidopsis increased plant tolerance to ABA, high salinity, and osmotic stress. By contrast, the CaKC2.1‐ silenced pepper fruits presented inhibited coloration and reduced carotenoids, soluble sugar, and potassium contents, and the expression of carotenoid synthesis‐related genes ( CaPSY , CaBCH , CaZEP , and CaCCS ) was also repressed. Collectively, these results suggest the positive role of CaKC2.1 in pepper fruit coloration and increase our understanding of K + channels in pepper.