Phytochromes A and B (phyA and phyB) are the far-red and red lights photoreceptors mediating many light responses in Arabidopsis thaliana.Brassinosteroid (BR) is a pivotal phytohormone regulating a variety of plant developmental processes including photomorphogenesis.It is known that phyB interacts with BES1 to inhibit its DNA-binding activity and repress BR signaling.Here, we show that far-red and red lights modulate DEEP OCEAN MINERALS BR signaling through phyA and phyB regulation of the stability of BIN2, a glycogen synthase kinase 3 (GSK3)-like kinase that phosphorylates BES1/BZR1 to inhibit BR signaling.The BIN2 gain-of-function mutant bin2-1 displays an enhanced photomorphogenic phenotype in both far-red and red lights.
phyA-enhanced accumulation of BIN2 promotes the phosphorylation of BES1 in far-red light.BIN2 acts genetically downstream from PHYA to regulate photomorphogenesis under far-red light.Both phyA and phyB interact directly with BIN2, which may promote the interaction Screens of BIN2 with BES1 and induce the phosphorylation of BES1.Our results suggest that far-red and red lights inhibit BR signaling through phyA and phyB stabilization of BIN2 and promotion of BES1 phosphorylation, which defines a new layer of the regulatory mechanism that allows plants to coordinate light and BR signaling pathways to optimize photomorphogenesis.