BRASSINAZOLE RESISTANT 1 delays photoperiodic flowering by repressing CONSTANS transcription.

Photoperiodic regulation of flowering time plays a critical role in plant reproductive success and crop yield. In Arabidopsis thaliana, the expression of the CONSTANS (CO) gene is closely regulated by day length and is modulated by both environmental and endogenous cues for precise control over flowering. Our findings reveal that the phytohormone brassinosteroid (BR) pathway represses flowering by inhibiting the expression of both CO and Flowering Locus T (FT). Additionally, we discovered that BRASSINAZOLE RESISTANT 1 (BZR1), a key transcription factor in the BR signaling pathway, directly binds to the proximal promoter region of CO to suppress its transcription during long days, thus regulating photoperiodic flowering. Genetically, BZR1 acts upstream of CO and FT to delay floral initiation depending on day length. Overall, our study reveals how a molecular module comprising BZR1-CO integrates signals from BR as well as photoperiodicity for appropriate adjustment of flowering time.