The CsFT-FD Complex Controls Flowering by Regulating CsAP1 and CsLFY in Saffron

Saffron (Crocus sativus L.) is a widely recognized medicinal and economic crop, valued primarily for the red stigmas that constitute its pharmaceutically active component. Flowering represents a critical agronomic trait, as it directly governs saffron yield. However, the molecular mechanisms underlying flowering regulation in saffron are not well studied. In this study, we identified a CsFT3-like-FD-AP1/LFY module involved in controlling flowering in saffron under indoor cultivation. Through transcriptomic and DAP-seq analysis, key floral identity genes CsAPETALA1 (CsAP1) and CsLEAFY (CsLFY) were identified as targets of the CsFT3-like-FD complex. Direct transcriptional regulation of CsAP1 and CsLFY by CsFT3-like-FD was further confirmed by dual-luciferase assays. Expression profiling revealed that CsAP1 is predominantly expressed in saffron leaves, tepals, and stamens, whereas CsLFY is mainly expressed in leaves and tepals. Both proteins localize to the nucleus. Ectopic expression of CsAP1 or CsLFY in Arabidopsis significantly accelerates flowering. Notably, CsAP1 overexpression additionally alters floral organ architecture, indicating its dual role in promoting flowering and regulating floral organ formation. Together, these findings underscore the essential role of the CsFT3-like-FD-AP1/LFY regulatory module in saffron and offer novel insights into flowering regulation in non-model monocot plants.