BASIC PENTACYSTEINE (BPC) family members are plant-specific GAGA-motif binding factors (GAFs) controlling multiple developmental processes of growth and propagation. BPCs recruit histone remodeling factors of repressive complexes involving in the transcriptional repression of downstream targets. Under day-night cycles, we found multiple BPC members are transcriptionally co-expressed with LIGHT-REGULATED WD1 (LWD1), which encodes a co-activator for the activation of central clock gene, CIRCADIAN CLOCK ASSOCIATED1 (CCA1). The co expression between BPCs and LWDs prompted us to investigate the role of BPCs in the circadian regulation. We revealed that BPC3, a member antagonized by the functional overlap of other BPCs in vegetative tissues aboveground, is ectopically expressed in the quadruple mutant of bpc1-1 bpc2 bpc4 bpc6. The ectopic BPC3 suppresses multiple clock genes including CCA1 in the mutant and the clock oscillation is therefore phase-delayed. Consequently, the expression peak of CONSTANS (CO) is delayed and the day-time CO level is insufficient to activate the expression of FLOWERING LOCUS T (FT). Intriguingly, even FT expression is obliterated, the mutant is still early-flowered due to that the ectopic BPC3 simultaneously suppresses the main floral repressor FLOWERING LOCUS C (FLC) of the autonomous pathway through direct binding to the FLC promoter. Taken together, our study reveals plant-specific GAFs tune the photoperiodic and autonomous floral promotion pathways concurrently to control the vegetative-to-reproductive transition.