Seminars

There is natural variation in epigenetic state both in mammals and plants, but the significance of this variation remains unclear. The FWA gene was identified as a late flowering epi-mutant in Arabidopsis thaliana. FWA is silenced by DNA methylation in vegetative tissue, but it is specifically demethylated in the central cell of the female ovule and continues to be expressed in the endosperm from the maternal copy. A sequence similar to the SINE retroelement found near the transcription start site is conserved in the genus Arabidopsis and is the target of DNA methylation in A. thaliana (Lippman et al. 2004, Fujimoto et al. 2008). In A. thaliana, FWA is stably silenced in vegetative tissue, but in the related species, FWA expression and DNA methylation levels vary in vegetative tissue. In this study, we examined vegetative FWA expression in these species. Variation of vegetative FWA expression correlated with differences of methylation at non-CG sites in the region upstream of the transcription start site in the SINE-like region, and we suggest that this region is the critical methylated region for FWA silencing. In A. thaliana, the FWA expression is affected by methylation in regions both upstream and downstream from the transcription start site. The critical methylated region may have spread during evolution by the acquisition of thaliana-specific large tandem repeats. Ectopic thaliana FWA expression causes a late flowering phenotype, but over-expression of lyrata FWA does not. Stable FWA silencing might result from the selection of the large tandem repeats during evolution to inhibit late flowering in A. thaliana

(English seminar)