Dear Editor,rnPlants utilize K+ ions to maintain hydrostatic pressure, drive irreversible cell expansion for growth, and facilitate reversible changes in guard cell volume that cause stomatal opening or closing.KAT1 is a voltage-dependent potassium channel from Arabidopsis thaliana that is mainly expressed in guard cells.KAT1 allows the influx of K+, leading to the swelling and opening of the stoma, and therefore plays a key role in regulating the aperture of stomatal pores on the surface of plant leaves.1-3 To understand the gating mechanism of plant K+ channels poses several challenges, despite many structural similarities between these plant K+ channels and mammalian Kv and Shaker channels.4 Remarkably, most voltage-gated ion channels, such as Na+(Nav),Ca2+ (Cav), and K+ (Kv) channels, open when the cell membrane is depolarized (when the voltage is positive inside relative to outside).Comparing with conventional depolarized K+ channels,KAT1 has a uniquely reversed voltage dependence: depolarization causes closing, and hyperpolarization causes opening.3 KAT1 thus falls into a rare class of hyperpolarization-activated channels,which include hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels in animals, and KAT and AKT channels in plants.