PT - JOURNAL ARTICLE AU - Uozumi, Nobuyuki AU - Kim, Eugene J. AU - Rubio, Francisco AU - Yamaguchi, Takao AU - Muto, Shoshi AU - Tsuboi, Akio AU - Bakker, Evert P. AU - Nakamura, Tatsunosuke AU - Schroeder, Julian I. TI - The <em>Arabidopsis HKT1</em> Gene Homolog Mediates Inward Na<sup>+</sup> Currents in <em>Xenopus laevis</em> Oocytes and Na<sup>+</sup> Uptake in <em>Saccharomyces cerevisiae</em> AID - 10.1104/pp.122.4.1249 DP - 2000 Apr 01 TA - Plant Physiology PG - 1249--1260 VI - 122 IP - 4 4099 - http://www.plantphysiol.org/content/122/4/1249.short 4100 - http://www.plantphysiol.org/content/122/4/1249.full SO - Plant Physiol.2000 Apr 01; 122 AB - The Na+-K+ co-transporter HKT1, first isolated from wheat, mediates high-affinity K+ uptake. The function of HKT1 in plants, however, remains to be elucidated, and the isolation of HKT1 homologs from Arabidopsis would further studies of the roles of HKT1 genes in plants. We report here the isolation of a cDNA homologous to HKT1 from Arabidopsis (AtHKT1) and the characterization of its mode of ion transport in heterologous systems. The deduced amino acid sequence of AtHKT1 is 41% identical to that of HKT1, and the hydropathy profiles are very similar.AtHKT1 is expressed in roots and, to a lesser extent, in other tissues. Interestingly, we found that the ion transport properties of AtHKT1 are significantly different from the wheat counterpart. As detected by electrophysiological measurements, AtHKT1 functioned as a selective Na+ uptake transporter inXenopus laevis oocytes, and the presence of external K+ did not affect the AtHKT1-mediated ion conductance (unlike that of HKT1). When expressed in Saccharomyces cerevisiae, AtHKT1 inhibited growth of the yeast in a medium containing high levels of Na+, which correlates to the large inward Na+ currents found in the oocytes. Furthermore, in contrast to HKT1, AtHKT1 did not complement the growth of yeast cells deficient in K+ uptake when cultured in K+-limiting medium. However, expression ofAtHKT1 did rescue Escherichia colimutants carrying deletions in K+ transporters. The rescue was associated with a less than 2-fold stimulation of K+uptake into K+-depleted cells. These data demonstrate that AtHKT1 differs in its transport properties from the wheat HKT1, and that AtHKT1 can mediate Na+ and, to a small degree, K+ transport in heterologous expression systems.