Plant GSK3 kinases: From multilayered regulation to precision engineering for crop improvement.

Plant glycogen synthase kinase 3 (GSK3) integrates development and environment. Unlike animals, plants have expanded this family: Arabidopsis has ten GSK3s and rice has nine. BIN2 was once seen as just a brake for brassinosteroid (BR) signaling. That view is now outdated. Four paradigms now define GSK3 function: (1) bidirectional regulation - it both destabilizes and stabilizes substrates; (2) multimodal control - phosphorylation, acetylation, oxidation, S-nitrosylation, and ubiquitination-dependent turnover; (3) subcellular localization as a functional switch; (4) direct application in crop improvement. We examine how GSK3 activity, stability, and localization are controlled, and propose an integrated model: a "modification code", protein abundance, localization, and non-covalent interactions together determine functional output. We also discuss how GSK3 interacts with its structural context and the cellular environment. Finally, we translate these findings into strategies for crop improvement, including species-specific modulation of this conserved growth regulator, divergent stress responses, and three precision engineering strategies: phosphosite editing, tissue-specific knockdown, and scaffold targeting. Our goal is to move from static gene catalogs to mechanistic frameworks and to provide a roadmap for harnessing GSK3 pleiotropy in trait-specific crop improvement.