User:Juliannaplace99/sandbox

Florigen is a systemically mobile signal that is synthesized in leaves and the transported via the phloem to the shoot apical meristem (SAM) where it initiates flowering. In Arabidopsis, the FLOWERING LOCUS T (FT) genes encode for the flowering hormone and in rice the hormone is encoded by Hd3a genes thereby making these genes orthologs. It was found though the use of transgenic plants that the Hd3a promoter in rice is located in the phloem of the leaf along with the Hd3a mRNA. However, the Hd3a protein is found in neither of these places but instead accumulates in the SAM which shows that Hd3a protein is first translated in leaves and then transported to the SAM via the phloem where floral transition is initiated; the same results occurred when looked at Arabidopsis. These results conclude that FT/Hd3a is the florigen signal that induces floral transition in plants.

Upon this conclusion, it became important to understand the process by which the FT protein causes floral transition once it reaches the SAM. The first clue came with looking at models from Arabidposis which suggested that a bZIP domain containing transcription factor, FD, is somehow interacting with FT to form a transcriptional complex that activates floral genes. . Studies using rice found that there is an interaction between Hd3a and OsFD1, homologs of FT and FD respectively, that is mediated by the 14-3-3 protein GF14c. The 14-3-3 protein acts as intracellular florigen receptor that interacts directly with Hd3a and OsFD1 to form a tri-protein complex called the florigen activation complex (FAC) because it is essential for florigen function. The FAC works to activate genes needed to initiate flowering at the SAM; flowering genes in Arabidopsis are AP1 and SOC1 and in rice the flowering gene is OsMADS15 (a homolog of AP1).