Dynamic and Basal Phosphorylation Landscapes of Abscisic Acid Signaling Revealed by Phosphoproteome Analysis in Arabidopsis

, respectively. Beyond known ABA signaling components, these datasets revealed numerous previously uncharacterized candidate proteins involved in metabolism, membrane transport, transcription, and cytoskeletal regulation. Integrative analysis uncovered a core set of candidate proteins oppositely regulated by SnRK2-mediated phosphorylation and ABI1-mediated dephosphorylation, defining a coordinated hierarchical network. These results indicate that the SnRK2-PP2C module functions not only in stress-induced ABA responses but also as a central regulator of phosphorylation homeostasis under basal conditions. This study provides a systematic framework for the global SnRK2-PP2C phosphorylation network and reframes ABA signaling as a dynamic homeostatic system.