title: Structure and transport mechanism of a high-affinity potassium uptake transporter from higher plants.
abstract: Potassium is the most abundant cation in higher plants and is crucial for plant nutrition, growth, tropisms, enzyme homeostasis and osmoregulation. K+ accumulation can be rate-limiting for agricultural production. K+ uptake from soils into roots is largely mediated by high-affinity K+ uptake (Km approximately 10-40 microM) (refs 1, 2, 5-7). But although K+ channels allow low-affinity K+ uptake, both the transport mechanism and structure of the high-affinity K+ nutrition pathway remain unknown. Here we use expression cloning to isolate a complementary DNA encoding a membrane protein (HKT1) from wheat roots which confers the ability to take up K+. The substrate affinity, saturation and cation selectivity of HKT1 correspond to hallmark properties of classical high-affinity K+ uptake in plants. The transport mechanism of HKT1 uses K(+)-H+ co-uptake. Expression of HKT1 is localized to specific root and leaf regions which represent primary sites for K+ uptake in plants. HKT1 is important for plant nutrition and could possibly contribute to environmental alkali metal toxicities.
authors.affiliation: Department of Biology, University of California, San Diego, La Jolla 92093-0116.
authors.forename: D P
authors.initials: DP
authors.lastname: Schachtman
authors.forename: J I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004247:DNA; D015870:Gene Expression; D017343:Genes, Plant; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012441:Saccharomyces cerevisiae; D027981:Symporters; D014908:Triticum / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; C088864:HKT1 protein, plant; D008565:Membrane Proteins; D010940:Plant Proteins; D027981:Symporters; D004247:DNA; D011188:Potassium