Fig. 1

CBL–CIPK pathway for maintaining ion homeostasis under high salinity and low-K⁺ conditions. Salt and low-K⁺ environmental conditions are perceived by unknown sensors, triggering different cytosolic Ca²⁺ signals. CBL4, CBL10, CBL1, and CBL9 perceive related Ca²⁺ signals; the first two proteins interact with CIPK24, while CBL1 and CBL9 interact with CIPK23. Plasma membrane Na⁺/H⁺ antiporter SOS1 is phosphorylated and activated by CBL4–CIPK24 in roots and by CBL10–CIPK24 in shoots, subsequently transporting Na⁺ out of the cell. The CBL1/9–CIPK23 complex phosphorylates K⁺ channel AKT1, which enhances K⁺ uptake under K⁺ deficient conditions. Only CBL4–CIPK24 pathway has been confirmed in rice. At, Arabidopsis; Os, rice.