The photoperiodic control of flowering in plants begins with the perception of seasonal changes in day length and consequential induction of a mobile floral stimulus in leaves. This stimulus called florigen is transported from leaves to the shoot apical meristem to provoke the initiation of floral meristems. Decades of efforts have identified that the proteins encoded by FLOWERING LOCUS T (FT) in Arabidopsis and its orthologs in other plant species are part of the long-sought florigen. Emerging evidence suggests that long-distance transport of FT towards the shoot apical meristem occurs through the phloem in a regulated manner. This review summarizes the recent advances in understanding florigen transport and discusses the proven and potential regulators required for this process.
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