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
Avicennia officinalis
KUP/HAK/KT transporter family gene,
AoKUP2
, which has high sequence similarity to its
Arabidopsis
ortholog
AtKUP2
. These genes were functionally characterized in mutant yeast cells and
Arabidopsis
plants. Both
AoKUP2
and
AtKUP2
were induced by salt stress, and
AtKUP2
was primarily induced in roots. Subcellular localization revealed that AoKUP2 and AtKUP2 are localized to the plasma membrane and mitochondria. Expression of
AtKUP2
and
AoKUP2
in
Saccharomyces cerevisiae
mutant strain (BY4741
trk1
Δ
::loxP trk2
Δ
::loxP
) helped to rescue the growth defect of the mutant under different NaCl and K
+
concentrations. Furthermore, constitutive expression of
AoKUP2
and
AtKUP2
conferred enhanced salt tolerance in
Arabidopsis
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
AtKUP2
expression. Our results suggest that AtKUP2 plays a key role in enhancing salt stress tolerance by maintaining cellular ion homeostasis.
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