Regulation of Expression by bHLH and WRKY Transcription Factors Helps to Confer Increased Salt Tolerance to Plants.

Potassium transporters play an essential role in maintaining cellular ion homeostasis, turgor pressure, and pH, which are critical for adaptation under salt stress. We identified a salt responsive KUP/HAK/KT transporter family gene, , which has high sequence similarity to its ortholog . These genes were functionally characterized in mutant yeast cells and plants. Both and were induced by salt stress, and was primarily induced in roots. Subcellular localization revealed that AoKUP2 and AtKUP2 are localized to the plasma membrane and mitochondria. Expression of and in mutant strain (BY4741 ΔΔ) helped to rescue the growth defect of the mutant under different NaCl and K concentrations. Furthermore, constitutive expression of and conferred enhanced salt tolerance in indicated by higher germination rate, better survival, and increased root and shoot length compared to the untreated controls. Analysis of Na and K contents in the shoots and roots showed that ectopic expression lines accumulated less Na and more K than the WT. Two stress-responsive transcription factors, bHLH122 and WRKY33, were identified as direct regulators of expression. Our results suggest that AtKUP2 plays a key role in enhancing salt stress tolerance by maintaining cellular ion homeostasis.