摘要ABSCISIC ACID-INSENSITIVE 4(ABI4)is a pivotal transcription factor which coordinates multiple aspects of plant growth and development as well as plant responses to environmental stresses.ABI4 has been shown to be involved in regulating seedling photomorphogenesis;however,the underlying mechanism remains elusive.Here,we show that the role of ABI4 in regulating photomorphogenesis is generally regulated by sucrose,but ABI4 promotes hypocotyl elongation of Arabidopsis seedlings under blue(B)light under all tested sucrose concen-trations.We further show that ABI4 physically inter-acts with PHYTOCHROME INTERACTING FACTOR 4(PIF4),a well-characterized growth-promoting tran-scription factor,and post-translationally promotes PIF4 protein accumulation under B light.Further analyses indicate that ABI4 directly interacts with the B light photoreceptors cryptochromes(CRYs)and inhibits the interactions between CRYs and PIF4,thus relieving CRY-mediated repression of PIF4 pro-tein accumulation.In addition,while ABI4 could di-rectly activate its own expression,CRYs enhance,whereas PIF4 inhibits,ABI4-mediated activation of the ABI4 promoter.Together,our study demon-strates that the ABI4-PIF4 module plays an important role in mediating CRY-induced B light signaling in Arabidopsis.