The flowering time gene FT and the floral transition

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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.
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