title: AtHKT1;1 mediates nernstian sodium channel transport properties in Arabidopsis root stelar cells.
abstract: The Arabidopsis AtHKT1;1 protein was identified as a sodium (Na⁺) transporter by heterologous expression in Xenopus laevis oocytes and Saccharomyces cerevisiae. However, direct comparative in vivo electrophysiological analyses of a plant HKT transporter in wild-type and hkt loss-of-function mutants has not yet been reported and it has been recently argued that heterologous expression systems may alter properties of plant transporters, including HKT transporters. In this report, we analyze several key functions of AtHKT1;1-mediated ion currents in their native root stelar cells, including Na⁺ and K⁺ conductances, AtHKT1;1-mediated outward currents, and shifts in reversal potentials in the presence of defined intracellular and extracellular salt concentrations. Enhancer trap Arabidopsis plants with GFP-labeled root stelar cells were used to investigate AtHKT1;1-dependent ion transport properties using patch clamp electrophysiology in wild-type and athkt1;1 mutant plants. AtHKT1;1-dependent currents were carried by sodium ions and these currents were not observed in athkt1;1 mutant stelar cells. However, K⁺ currents in wild-type and athkt1;1 root stelar cell protoplasts were indistinguishable correlating with the Na⁺ over K⁺ selectivity of AtHKT1;1-mediated transport. Moreover, AtHKT1;1-mediated currents did not show a strong voltage dependence in vivo. Unexpectedly, removal of extracellular Na⁺ caused a reduction in AtHKT1;1-mediated outward currents in Columbia root stelar cells and Xenopus oocytes, indicating a role for external Na⁺ in regulation of AtHKT1;1 activity. Shifting the NaCl gradient in root stelar cells showed a Nernstian shift in the reversal potential providing biophysical evidence for the model that AtHKT1;1 mediates passive Na⁺ channel transport properties.
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California, United States of America.
authors.forename: Shaowu
authors.initials: S
authors.lastname: Xue
authors.forename: Xuan
authors.initials: X
authors.lastname: Yao
authors.forename: Wei
authors.initials: W
authors.lastname: Luo
authors.forename: Deepa
authors.initials: D
authors.lastname: Jha
authors.forename: Mark
authors.initials: M
authors.lastname: Tester
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Horie
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D018408:Patch-Clamp Techniques; D018517:Plant Roots / Q000166:cytology* / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D027981:Symporters / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; C490286:HKT1 protein, Arabidopsis; D015222:Sodium Channels; D027981:Symporters; D012964:Sodium