Temperature-Responsive FPF1 Homologs Regulate Floral Transition in Saffron

Saffron (Crocus sativus L.) is an economically important plant valued for the spice derived from its flower, specifically the stigma. As a thermoperiodic species, its flowering is primarily regulated by temperature cues. Although previous morphophysiological studies have explored this phenomenon, the molecular mechanisms underlying temperature-mediated floral induction in saffron remain largely unknown. In this study, we identify and functionally characterize two FLOWERING PROMOTING FACTOR 1 (FPF1)-like genes, CsatFPF1.1 and CsatFPF1.2, as key thermoresponsive regulators of floral initiation. They possess conserved motifs, localize to the nucleus, and exhibit flower meristem-specific expression, with marked upregulation during the floral induction phase under ambient high temperatures. Ectopic expression in Arabidopsis thaliana resulted in early flowering, while virus-induced gene silencing (VIGS) in saffron corms suppressed flowering, highlighting their essential role. CsatFPF1.1 and CsatFPF1.2 positively regulates flowering by upregulating AtFT expression in Arabidopsis, whereas its silencing in saffron downregulates CsatFT3. This work presents in planta functional validation of flowering regulators in saffron, offering new insights into its temperature-dependent flowering pathway and providing valuable targets for genetic and biotechnological approaches to improve saffron yield and adaptability.