The flowering-time gene FT and the floral transition Takashi Araki Department of Botany, Graduate. School of Science, Kyoto University, Kyoto 6068502, Japan. Flowering in Arabidopsis is promoted by several interacting pathways. A photoperioddependent pathway mediates signals from photoreceptors to a transcription factor gene CONSTANS (CO), which activates downstream genes such as FT and LEAFY (LFY). Photoperiod-independent pathways, mediated by genes such as FCA, also activate FT and LFY. Simultaneous over-expression of FT and LFY causes conversion of the whole shoot into a single terminal flower with one or two bracts, suggesting that the combined activity of both genes strongly promotes flowering. These two genes act in parallel pathways. FT primarily affects floral transition, while LFY affects mainly floral fate specification of meristem and plays a crucial role in transcriptional regulation of organ identity genes. The pathway downstream of FT, however, remains to be elucidated. The late-flowering gene FD is a good candidate of genes acting downstream of FT. The FD activity seems to be required for the precocious-flowering phenotype of 35S::FT. However, double mutant phenotype and genetic interaction with other genes suggested that FD is also involved in FT-independent pathway(s). Characterization of fd-1 mutant and progress toward map-based cloning of the FD locus will be presented. Another candidate which may be involved in the FT function is a gene identified by a specific dominant enhancer of 35S::FT. The mutation alone causes slightly earlier flowering in both LD and SD conditions with no apparent seedling phenotype, suggesting that the gene is specifically involved in flowering. Characterization of this mutant and progress toward map-based cloning will also be presented.