Functional Analysis of the KUP9 Gene in Response to Drought Stress in Oilseed Rape

Abstract

Potassium transporters play critical roles in the drought stress response of oilseed rape. This study elucidates the molecular characteristics, transcriptional regulation, and mechanisms of potassium homeostasis remodeling of the KUP9 gene. The protein encoded by KUP9 contains 11 to 12 transmembrane helices and belongs to the KUP/HAK/KT family. The ABRE and DRE elements in the promoter region mediate the hierarchical regulation of KUP9 by the SnRK2‑AREB and DREB2A pathways, with the peak transcript level in root tissues reaching 5.6 times that of the control. Overexpression of KUP9 maintained cytosolic potassium concentration at 82±6 mM, promoted potassium retention in guard cells to increase the stomatal aperture reduction by 28%, and induced the accumulation of proline and trehalose by 2.4‑fold and 1.9‑fold, respectively. These results indicate that KUP9 enhances drought tolerance in oilseed rape by maintaining potassium homeostasis, optimizing stomatal movement, and promoting compatible solute accumulation.