Cis-regulatory architecture downstream of FLOWERING LOCUS T underlies quantitative control of flowering in Arabidopsis thaliana

BACKGROUND: The FLOWERING LOCUS T (FT) gene is a central integrator of floral induction in Arabidopsis thaliana, with its precise expression controlled by complex transcriptional networks. While upstream regulatory regions are well-studied, the role of downstream cis-regulatory elements in modulating FT expression remains poorly characterized. RESULTS: Systematic dissection of the FT downstream region in its native chromosomal context using CRISPR/Cas9-mediated genome editing provides genetic evidence that a 2.3-kb sequence, encompassing the Block E enhancer immediately adjacent to the FT coding sequence, is essential for proper FT expression and timely flowering. Fine-scale deletions within Block E reveal that a 63-bp sequence containing one CCAAT-box and one G-box, both closely spaced, forms a core functional module, whereas other conserved motifs contribute modestly in a context-dependent manner. Strikingly, a cryptic CCAAT-box module downstream of Block E that becomes active when repositioned. This coincides with increased transcription factor occupancy and local chromatin accessibility. CONCLUSIONS: Our work reveals that quantitative FT expression and flowering time are governed by the spatial organization and chromatin context of downstream cis-regulatory elements. The positional sensitivity and modular logic of these elements provide framework for understanding and engineering quantitative gene regulation through targeted cis-regulatory design, a concept broadly applicable across diverse developmental systems.