BrFLD integrates histone demethylation and florigen activation complex to regulate flowering in Caixin (Brassica rapa var. parachinensis)

Flowering constitutes a pivotal aspect of plant reproduction and the survival of populations, being governed by both environmental and endogenous cues. Histone modifications serve as a key epigenetic mechanism that precisely modulates flowering timing through the alteration of chromatin accessibility. In this study, we identified BrFLD, a homolog of the Arabidopsis histone demethylase FLD, in Caixin ( Brassica rapa var. parachinensis ). BrFLD is characterized by its apex-specific expression and localization in the nucleus. Heterologous overexpression of BrFLD in Arabidopsis resulted in accelerated flowering, whereas its silencing in Caixin led to delayed flowering, increased accumulation of H3K4me2, and elevated transcript levels of the floral repressors BrFLC3/5 . Mechanistically, the bZIP transcription factors BrFD1/2/3 directly activate BrFLD expression through their binding to its promoter, with BrFD1/2 additionally augmenting this activation via interactions with BrFT1 and Br14–3-3a. Our results delineate BrFLD as a critical mediator that links histone demethylation with the florigen activation complex (FAC)-mediated regulation of flowering in Caixin, thereby offering novel insights into the epigenetic modulation of crop phenology. • BrFLD is a positive flowering regulator; its silencing delays flowering, upregulates BrFLC3/5 , and increases H3K4me2 at these loci. • bZIP factors BrFD1/2/3 directly activate BrFLD by binding its promoter, linking florigen to this epigenetic regulator. • A novel complex (BrFD1/2-BrFT1-Br14–3–3a) enhances BrFLD transcription, linking the florigen activation complex and autonomous pathway.