Antagonism between sugar-dependent O-fucosylation and BIN2-mediated phosphorylation regulates metabolism and growth in Arabidopsis

Coordinating sugar sensing, hormone signaling, and carbon metabolism is crucial for plant growth and environmental acclimation. Brassinosteroid (BR)-dependent phosphorylation and sugar-dependent O-glycosylation modify overlapping sets of proteins, but how these modifications co-regulate protein functions remains unknown. Here, we show that SPINDLY (SPY)-catalyzed O-fucosylation competes with BIN2-mediated phosphorylation and antagonistically regulates phosphoenolpyruvate carboxykinase 1 (PCK1), a key gluconeogenic enzyme. SPY associates with and O-fucosylates PCK1 within a peptide containing Ser-62 and Thr-66, two BIN2 phosphorylation sites that regulate PCK1 activity, preventing its phosphorylation by BIN2. PCK1 O-fucosylation and phosphorylation exclude each other and oppositely affect PCK1 activity in vivo. The spy mutants show increased PCK1 phosphorylation, reduced PCK activity, and impaired hypocotyl elongation; BR or BIN2 inhibitor treatments suppressed these phenotypes, indicating that these spy effects result from increased BIN2 phosphorylation. Together, these results reveal functional antagonism between SPY/O-fucosylation and BIN2/phosphorylation in regulating metabolism and growth