Figure 3.

Stochastic switching mechanism underlies the quantitative nature of vernalization. (A) During cold, H3K27me3 quantitatively accumulates in the nucleation region of the FLC gene, indicated schematically below each graph, with increasing weeks of cold (top row of figure). (B) After cold, the nucleated H3K27me3 causes some cells to switch to a silenced state with high levels of H3K27me3 blanketing the gene. This epigenetic switch is cell-autonomous. (C) The quantitative nature of the vernalization response is due to an increasing number of cells switching to a silenced state after increasing cold exposure. Each cell is indicated by a square. (Figure courtesy of Dr. Jie Song.)