title: The high affinity K+ transporter AtHAK5 plays a physiological role in planta at very low K+ concentrations and provides a caesium uptake pathway in Arabidopsis.
abstract: Caesium (Cs(+)) is a potentially toxic mineral element that is released into the environment and taken up by plants. Although Cs(+) is chemically similar to potassium (K(+)), and much is known about K(+) transport mechanisms, it is not clear through which K(+) transport mechanisms Cs(+) is taken up by plant roots. In this study, the role of AtHAK5 in high affinity K(+) and Cs(+) uptake was characterized. It is demonstrated that AtHAK5 is localized to the plasma membrane under conditions of K(+) deprivation, when it is expressed. Growth analysis showed that AtHAK5 plays a role during severe K(+) deprivation. Under K(+)-deficient conditions in the presence of Cs(+), Arabidopsis seedlings lacking AtHAK5 had increased inhibition of root growth and lower Cs(+) accumulation, and significantly higher leaf chlorophyll concentrations than wild type. These data indicate that, in addition to transporting K(+) in planta, AtHAK5 also transports Cs(+). Further experiments showed that AtHAK5 mediated Cs(+) uptake into yeast cells and that, although the K(+) deficiency-induced expression of AtHAK5 was inhibited by low concentrations of NH(4)(+) in planta, Cs(+) uptake by yeast was stimulated by low concentrations of NH(4)(+). Interestingly, the growth of the Arabidopsis atakt1-1 mutant was more sensitive to Cs(+) than the wild type. This may be explained, in part, by increased expression of AtHAK5 in the atakt1-1 mutant. It is concluded that AtHAK5 is a root plasma membrane uptake mechanism for K(+) and Cs(+) under conditions of low K(+) availability.
authors.affiliation: Donald Danforth Plant Science Center, 975 N. Warson Road, St Louis, MO 63132, USA.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Qi
authors.forename: Corrina R
authors.initials: CR
authors.lastname: Hampton
authors.forename: Ryoung
authors.initials: R
authors.lastname: Shin
authors.forename: Bronwyn J
authors.initials: BJ
authors.lastname: Barkla
authors.forename: Philip J
authors.initials: PJ
authors.lastname: White
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Schachtman
mesh_terms: D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002586:Cesium / Q000378:metabolism*; D005816:Genetic Complementation Test; D018517:Plant Roots / Q000254:growth & development*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D027961:Potassium-Hydrogen Antiporters; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D027981:Symporters / Q000378:metabolism*; D015854:Up-Regulation; D015003:Yeasts / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D015221:Potassium Channels; D027961:Potassium-Hydrogen Antiporters; D000644:Quaternary Ammonium Compounds; D027981:Symporters; C501258:potassium transporter, Arabidopsis; C074500:AKT1 protein, Arabidopsis; D002586:Cesium; D011188:Potassium