AtCHX13 is a plasma membrane K⁺ transporter

Potassium (K⁺) homeostasis is essential for diverse cellular processes, although how various cation transporters collaborate to maintain a suitable K⁺ required for growth and development is poorly understood. The Arabidopsis (Arabidopsis thaliana) genome contains numerous cation:proton antiporters (CHX), which may mediate K⁺ transport; however, the vast majority of these transporters remain uncharacterized. Here, we show that AtCHX13 (At2g30240) has a role in K⁺ acquisition. AtCHX13 suppressed the sensitivity of yeast (Saccharomyces cerevisiae) mutant cells defective in K⁺ uptake. Uptake experiments using ⁸⁶Rb⁺ as a tracer for K⁺ demonstrated that AtCHX13 mediated high-affinity K ⁺ uptake in yeast and in plant cells with a K_m of 136 and 196 μM, respectively. Functional green fluorescent protein-tagged versions localized to the plasma membrane of both yeast and plant. Seedlings of null chx13 mutants were sensitive to K⁺ deficiency conditions, whereas overexpression of AtCHX13 reduced the sensitivity to K⁺ deficiency. Collectively, these results suggest that AtCHX13 mediates relatively high-affinity K⁺ uptake, although the mode of transport is unclear at present. AtCHX13 expression is induced in roots during K⁺-deficient conditions. These results indicate that one role of AtCHX13 is to promote K ⁺ uptake into plants when K⁺ is limiting in the environment.