Natural variation in autumn FLC levels, rather than epigenetic silencing, aligns vernalization to different climates

Plants monitor temperatures over long timescales to assess seasons and time developmental transitions. In Arabidopsis thaliana , winter is registered during vernalization through the temperature-dependent repression and epigenetic silencing of floral repressor FLOWERING LOCUS C (FLC) . Natural Arabidopsis accessions show considerable variation in vernalization, however which aspect of the FLC repression mechanism is most important for adaptation to different climates is not clear. By analyzing FLC silencing in natural variants throughout winter in three field sites, we find that FLC starting levels and early phases of silencing are the major variables underlying vernalization response, rather than establishment of epigenetic silencing. This results in an intricate interplay between promotion and delay of flowering to balance survival, and through a post-vernalization effect of FLC , reproductive effort via branch production. These data reveal how non-coding FLC variation aligns vernalization response to different climatic conditions and year-on-year fluctuations in natural temperature profiles. Impact Statement Alleles of the major floral repressor vary in their initial expression to underpin the ability of Arabidopsis to survive year-on-year climatic fluctuations.