Figure 2. Phloem-mobile signals in shoot development.

(A) Transition to flowering: FT and its homologs are expressed in the leaves in a photoperiod-controlled mechanism through GIGANTEA (GI), other circadian clock components and CO. FT and FT-like proteins, as well as FT mRNA transcripts, are transported in the phloem to the SAM to promote the transition from vegetative to reproductive growth. FT interacts with FD to promote flowering, whereas ATC, a second mobile flowering regulator, competes with FT to inhibit flowering. (B) The FAC comprises FT, 14-3-3 protein, and the TF FD. Complex formation and binding to DNA is mediated by interaction with PtdCho, as shown by the cartoon of the proposed structure from Nakamura et al. [60]. Phytohormones GAs, CKs, and ethylene (C₂H₂) also play a role in flowering in some plant species. Other FT-like proteins, such as SFT (tomato) and FT1 (cotton), not only act in flowering but also in leaf maturation, termination, and abscission signaling. (C) Tuber formation: BEL5, 11, and 29 and POTH1 mRNA, as well as SP6A protein and miR156 and 172, move in the SE of the phloem to stolon tissue, where they regulate tuber development. A BEL5–POTH1 complex, SP6A, miR156 and miR172 promote tuber formation, whereas BEL11 and BEL29 suppress it. Abbreviations, plants species and references for all compounds are detailed in Table 1.