The cytosolic domain of AKT1 potassium channel includes a docking site for CIPK23 protein kinase

Abstract

Plant growth depends on the maintenance of the adequate intracellular levels of potassium ion (K+). Different abiotic stresses threaten this homeostasis, thus, the characterization of the molecules involved in the regulation of cytoplasmic K+ concentration is important as they could be targeted for plant crop improvement. The families of 10 Calcineurin B like (CBL) calcium sensors and 26 CBL-Interacting Protein Kinases (CIPK) decode the calcium signals elicited by stress and regulate different ion channels and transporters involved in the control of K+ fluxes in plants. Nevertheless, the detailed molecular mechanisms balancing specificity and versatility to the system require investigation. Here, we show that the cytosolic domain of t he inwardrectifier K+ channel (AKT1) harbors a non-canonical ankyrin domain which is not essential for channel function but serves as a docking site for its regulator, the CIPK23 protein kinase. Mutations on this domain impair kinase channel association. This interaction is not strong enough to ensure signal specificity per se but should contribute to the formation of a multivalent complex between CIPK23/CBL1 and AKT1 in the membrane vicinity for the proper regulation of K+ transport.