Plants 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.
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