The control of flowering in time and space

The transition to flowering is one of the most important developmental decisions made by plants. Classical studies have highlighted the importance of photoperiod in controlling flowering time. More recently, the identification of mutants specifically affected in the photoperiod pathway in the model system Arabidopsis thaliana has enabled the flowering time pathways to be placed in a molecular context. This review highlights recent advances in understanding how photoperiod signals (perceived in the leaves) act at the apex of the plant where the floral stimulus is perceived. The photoperiod pathway acts predominantly through the gene CONSTANS to activate the small signalling molecule FT. While FT transcription is induced in the leaves, it is essential that FT protein is present at the apex of the plant. FT at the apex interacts with the transcription factor FD to induce flowering.