Sodium-driven potassium uptake by the plant potassium transporter HKT1 and mutations conferring salt tolerance.
Sodium (Na+) at high millimolar concentrations in soils is toxic to most higher plants and severely reduces agricultural production worldwide. However, the molecular mechanisms for plant Na+ uptake remain unknown. Here, the wheat root high-affinity potassium (K+) uptake transporter HKT1 was shown to function as a high-affinity K(+)-Na+ cotransporter. High-affinity K+ uptake was activated by micromolar Na+ concentrations; moreover, high-affinity Na+ uptake was activated by K+ (half-activation constant, 2.8 microM K+). However, at physiologically detrimental concentrations of Na+, K+ accumulation mediated by HKT1 was blocked and low-affinity Na+ uptake occurred (Michaelis constant, approximately 16 mM Na+), which correlated to Na+ toxicity in plants. Point mutations in the sixth putative transmembrane domain of HKT1 that increase Na+ tolerance were isolated with the use of yeast as a screening system. Na+ uptake and Na+ inhibition of K+ accumulation indicate a possible role for HKT1 in physiological Na+ toxicity in plants.
Rubio
F
F
Department of Biology, University of California, San Diego, La Jolla 92093-0116, USA.
Gassmann
W
W
Schroeder
J I
JI
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism* / Q000633:toxicity*; D013054:Spectrophotometry, Atomic; D027981:Symporters; D014981:Xenopus; D015003:Yeasts / Q000378:metabolism
D002352:Carrier Proteins; D027682:Cation Transport Proteins; C088864:HKT1 protein, plant; D008565:Membrane Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; D027981:Symporters; D012964:Sodium; D012413:Rubidium; D011188:Potassium