CHX 14 is a plasma membrane K ‐efflux transporter that regulates K + redistribution in A rabidopsis thaliana

Potassium ( K + ) is essential for plant growth and development, yet the molecular identity of many K + transporters remains elusive. Here we characterized cation/ H + exchanger ( CHX ) 14 as a plasma membrane K + transporter. CHX 14 expression was induced by elevated K + and histochemical analysis of CHX 14 promoter :: GUS transgenic plants indicated that CHX 14 was expressed in xylem parenchyma of root and shoot vascular tissues of seedlings. CHX 14 knockout ( chx14 ) and CHX 14 overexpression seedlings displayed different growth phenotypes during K + stress as compared with wild‐type seedlings. Roots of mutant seedlings displayed higher K + uptake rates than wild‐type roots. CHX 14 expression in yeast cells deficient in K + uptake renders the mutant cells more sensitive to deficiencies of K + in the medium. CHX 14 mediates K + efflux in yeast cells loaded with high K + . Uptake experiments using 86 R b + as a tracer for K + with both yeast and plant mutants demonstrated that CHX 14 expression in yeast and in planta mediated low‐affinity K + efflux. Functional green fluorescent protein ( GFP )‐tagged versions of CHX 14 were localized to both the yeast and plant plasma membranes. Taken together, we suggest that CHX 14 is a plasma membrane K + efflux transporter involved in K + homeostasis and K + recirculation.