Phosphorylation of GhSKD1 by GhCIPK6D1 regulates potassium efflux during the drought response in cotton

The calcineurin B-like (CBL)-interacting protein kinase (CIPK) signaling network is the core regulatory node in the response to abiotic stress in plants; it regulates plant homeostasis by regulating various proteins mediating ion transport. However, there are few reports on CIPK-mediated ion transporters in the cotton (Gossypium hirsutum) response to drought stress. Through yeast two-hybrid assays, we identified SUPPRESSOR OF K+ TRANSPORT GROWTH DEFECT 1 (GhSKD1), which interacts with GhCIPK6D1. GhSKD1 was significantly up-regulated after drought stress, while GhSKD1 localized to the cell membrane and nucleus. Functional studies revealed that GhSKD1 positively regulates K+ efflux, thus enhancing drought tolerance in cotton. Genetic and biochemical evidence showed that the phosphorylation of GhSKD1 by GhCIPK6D1 mediates K+ influx in guard cells, thereby regulating stomatal aperture and drought tolerance in cotton. GhSKD1 represents a previously uncharacterized protein that mediates potassium ion transport during the drought stress response. This finding identifies another target of CIPK regulation in the CPL-CIPK signaling network and provides insights into the mechanisms of drought tolerance in plants.