Abscisic acid triggers the endocytosis of the Arabidopsis KAT1 K+ channel and its recycling to the plasma membrane

Membrane vesicle traffic to and from the plasma membrane is essential for cellular homeostasis in all eukaryotes [1-3]. In plants, constitutive traffic to and from the plasma membrane has been implicated in maintaining the population of integral plasma-membrane proteins and its adjustment to a variety of hormonal and environmental stimuli [2, 3]. However, direct evidence for evoked and selective traffic has been lacking. Here, we report that the hormone abscisic acid (ABA), which controls ion transport and transpiration in plants under water stress [4, 5], triggers the selective endocytosis of the KAT1 K+ channel protein in epidermal and guard cells. Endocytosis of the K+ channel from the plasma membrane initiates in concert with changes in K channel activities evoked by ABA and leads to sequestration of the K+ channel within an endosomal membrane pool that recycles back to the plasma membrane over a period of hours. Selective K channel endocytosis, sequestration, and recycling demonstrates a tight and dynamic control of the population of K+ channels at the plasma membrane as part of a key plant signaling and response mechanism, and the observations point to a role for channel traffic in adaptive changes in the capacity for osmotic solute flux of stomatal guard cells [5, 6].