Cloning and functional characterization of the high-affinity K+ transporter HAK1 of pepper

High-affinity K+ uptake in plants plays a crucial role in K+ nutrition and different systems have been postulated to contribute to the high-affinity K+ uptake. The results presented here with pepper (Capsicum annum) demonstrate that a HAK1-type transporter greatly contributes to the high-affinity K+ uptake observed in roots. Pepper plants starved of K+ for 3 d showed high-affinity K+ uptake (K-m of 6 muM K+) that was very sensitive to NH4+ and their roots expressed a high-affinity K+ transporter, CaHAK1, which clusters in group I of the KT/HAK/KUP family of transporters. When expressed in yeast (Saccharomyces cerevisiae), CaHAK1 mediated high-affinity K+ and Rb+ uptake with K-m values of 3.3 and 1.9 muM, respectively. Rb+ uptake was competitively inhibited by micromolar concentrations of NH4+ and Cs+, and by millimolar concentrations of Na+.