Flower power

The timing of flowering in plants is affected by a wide range of hormonal, environmental and genetic factors. The semidominant fwa mutants are delayed in the transition to flowering. In the October Molecular Cell, Soppe et al. use positional cloning to isolate the Arabidopsis FWA gene, which encodes a homeodomain-containing protein (Molecular Cell 2000, 6:791-802). The late-flowering phenotype of the fwa mutants is caused by gain-of-function epi-alleles. Soppe et al. could find no differences in the genomic DNA sequence of the FWA gene. They show, however, that expression of the FWA gene is suppressed in mature wild-type plants because of extensive CG methylation and that ectopic expression in fwamutants is characterized by stable hypomethylation of directly repeated sequences in the 5' region of the gene. These results provide insights into epigenetic regulation and represent good news for florists trying to understand the timing of flowering.