Figure 7.

A hypothesized schematic model of the novel roles of SRK2D/E/I and CIPK26/3/9/23 in plant growth under high external Mg²⁺ concentrations in Arabidopsis. Under water deficit stress conditions, subclass III SnRK2s (SRK2D, SRK2I, and SRK2E/OST1) are activated by high levels of ABA, and they then modulate the activities of downstream targets, including transcription factors, such as AREB/ABFs and channels (e.g. SLAC1). Under high external Mg²⁺ concentrations, subclass III SnRK2s, in response to basal levels of ABA, play a key role in plant growth while interacting with CIPK26/3/9/23. Subclass III SnRK2s and CIPK26/3/9/23 function as key modulators of the susceptibility to shoot growth inhibition in response to increased external Mg²⁺ concentrations (Mg²⁺ susceptibility) probably through phosphorylating and, thus, modulating downstream targets, which are assumed to modulate intracellular Mg²⁺ transport and maintain Mg²⁺ homeostasis. Dashed lines indicate possible but not confirmed routes.