The High-Affinity Potassium Transporter EpHKT1;2 From the Extremophile Mediates Salt Tolerance.

To survive salt stress, plants must maintain a balance between sodium and potassium ions. High-affinity potassium transporters (HKTs) play a key role in reducing Na toxicity through K uptake. (formerly known as ), a halophyte closely related to , has two genes that encode EpHKT1;1 and EpHKT1;2. In response to high salinity, the transcript level increased rapidly; by contrast, the transcript increased more slowly in response to salt treatment. Yeast cells expressing EpHKT1;2 were able to tolerate high concentrations of NaCl, whereas EpHKT1;1-expressing yeast cells remained sensitive to NaCl. Amino acid sequence alignment with other plant HKTs showed that EpHKT1;1 contains an asparagine residue (Asn-213) in the second pore-loop domain, but EpHKT1;2 contains an aspartic acid residue (Asp-205) at the same position. Yeast cells expressing EpHKT1;1, in which Asn-213 was substituted with Asp, were able to tolerate high concentrations of NaCl. In contrast, substitution of Asp-205 by Asn in EpHKT1;2 did not enhance salt tolerance and rather resulted in a similar function to that of AtHKT1 (Na influx but no K influx), indicating that the presence of Asn or Asp determines the mode of cation selectivity of the HKT1-type transporters. Moreover, plants (Col-) overexpressing showed significantly higher tolerance to salt stress and accumulated less Na and more K compared to those overexpressing or . Taken together, these results suggest that EpHKT1;2 mediates tolerance to Na ion toxicity in and is a major contributor to its halophytic nature.