LNK1/2 and COR27/28 Regulate Arabidopsis Photoperiodic Flowering in FKF1-Dependent and -Independent Pathways

The circadian clock allows plants to anticipate daily and seasonal environmental changes, thereby optimizing photoperiod-dependent flowering. While core clock components such as LNK1 and LNK2, as well as COR27 and COR28, have been implicated in photoperiodic flowering in Arabidopsis, their specific roles and interactions remain poorly understood. Here, genetic analysis revealed that LNK1/2 act upstream of COR27/28 under long-day (LD) conditions and contribute slight additively under short-day (SD) conditions. LNK1/2 directly bind the FKF1 promoter to promote its transcriptiontg, leading to upregulation of FT and floral induction. By contrast, COR27/28 enhance FT expression through an FKF1-independent mechanism. Transcriptional and protein-level assays, including qRT-PCR and split-luciferase complementation, revealed that both LNK1/2 and COR27/28 are regulated by photoperiod and form a protein complex enriched near ZT12. These findings suggest coordinated regulation of flowering via both shared and distinct pathways. Together, our results demonstrate that LNK1/2 and COR27/28 integrate photoperiodic signals to regulate FT expression through FKF1-dependent and -independent mechanisms, revealing a new layer of circadian control over seasonal flowering.