TsHKT1;2, a HKT1 homolog from the extremophile Arabidopsis relative Thellungiella salsuginea, shows K(+) specificity in the presence of NaCl

Zahir Ali, Hyeong Cheol Park, Akhtar Ali, Dong-Ha Oh, Rashid Aman, Anna Kropornicka, Hyewon Hong, Wonkyun Choi, Woo Sik Chung, Woe-Yeon Kim, Ray A Bressan, Hans J Bohnert, Sang Yeol Lee, Dae-Jin Yun
Plant Physiology 2012, 158 (3): 1463-74
Cellular Na(+)/K(+) ratio is a crucial parameter determining plant salinity stress resistance. We tested the function of plasma membrane Na(+)/K(+) cotransporters in the High-affinity K(+) Transporter (HKT) family from the halophytic Arabidopsis (Arabidopsis thaliana) relative Thellungiella salsuginea. T. salsuginea contains at least two HKT genes. TsHKT1;1 is expressed at very low levels, while the abundant TsHKT1;2 is transcriptionally strongly up-regulated by salt stress. TsHKT-based RNA interference in T. salsuginea resulted in Na(+) sensitivity and K(+) deficiency. The athkt1 mutant lines overexpressing TsHKT1;2 proved less sensitive to Na(+) and showed less K(+) deficiency than lines overexpressing AtHKT1. TsHKT1;2 ectopically expressed in yeast mutants lacking Na(+) or K(+) transporters revealed strong K(+) transporter activity and selectivity for K(+) over Na(+). Altering two amino acid residues in TsHKT1;2 to mimic the AtHKT1 sequence resulted in enhanced sodium uptake and loss of the TsHKT1;2 intrinsic K(+) transporter activity. We consider the maintenance of K(+) uptake through TsHKT1;2 under salt stress an important component supporting the halophytic lifestyle of T. salsuginea.

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