|
Figure 1
Multiple developmental pathways for flowering in Arabidopsis: photoperiodism, the autonomous (leaf number) and vernalization (low temperature) pathways, the energy (sucrose) pathway, and the gibberellin pathway. The photoperiodic pathway is located in the leaves and involves the production of a transmissible floral stimulus, FT protein. In LDPs such as Arabidopsis, FT protein is produced in the phloem in response to CO protein accumulation under long days. It is then translocated via sieve tubes to the apical meristem. In SDPs such as rice, the transmissible floral stimulus Hd3a protein accumulates when the repressor protein, Hd1, is not produced under short days, and the Hd3a protein is translocated via the phloem to the apical meristem. In Arabidopsis, FT binds to FD, and the FT/FD protein complex activates the AP1 and SOC1 genes, which trigger LFY gene expression. LFY and AP1 then trigger the expression of the floral homeotic genes. The autonomous (leaf number) and vernalization (low temperature) pathways act in the apical meristem to negatively regulate FLC, a negative regulator of SOC1. The sucrose and gibberellin pathways, also localized to the meristem, promote SOC1 expression. (After Blázquez 2005.) |
