Advances in the HAK/KUP/KT Potassium Transporter Family in Regulating Na+/K+ Homeostasis and Salt Tolerance in Plants

Soil salinization severely threatens global agricultural sustainability. A key physiological mechanism underpinning plant salt tolerance is the maintenance of Na+/K+ homeostasis. The HAK/KUP/KT family of high-affinity potassium transporters plays a central role in plant responses to both potassium deficiency and salinity stress. This review systematically outlines the classification, evolutionary relationships, and functional specialization of this transporter family across diverse plant species. We focus on the multi-layered regulatory network that sustains Na+/K+ balance under salt stress, including calcium signaling transduced through the CBL-CIPK module, transcriptional control by transcription factors and epigenetic modifications, and post-translational regulation via phosphorylation, ubiquitination, and dynamic trafficking. Recent functional analyses in crops and woody plants highlight functional diversity and adaptive evolution. Notably, certain transporters from halophytes exhibit specialized roles that, when expressed in glycophytes, can paradoxically reduce salt tolerance, underscoring species-specific functional divergence. As a central hub integrating potassium nutrition and stress signaling, the HAK/KUP/KT family represents a promising target for genetic improvement. Future strategies employing gene editing, synthetic promoters, and synthetic biology hold promise for developing salt-tolerant, high-yielding crop varieties.