With temperatures soaring above 100°F in many parts of the U.S., it can be awfully hard to remember what last winter was like. But thanks to histone modifications, many plants have a built-in memory of cold periods—which is important for flowering.
Plants not only remember that they went through a cold period, but they also remember how long it lasted. Enduring a cold period, or vernalization, makes plants competent to flower when they finally experience the warmth of spring, and as it turns out one of our favorite repressive histone mods, H3K27me3, is at the heart of it all.Researchers in the U.K. knew that epigenetics was involved, but they wondered how exactly this “quantitative” memory formed.
Here’s a little bit of what they found when they combined data from chromatin immunoprecipitation (ChIP) experiments, computer modeling, and reporter gene assays:
- As the period of cold increased, a localized “nucleation” peak of H3K27me3 built up at a small region of the FLC gene that represses flowering. (Reduced FLC expression prepares plants to flower in the spring.) Also, as plants warmed up, H3K27me3 spread out over the rest of the gene according to the time they were in the cold.
- Mathematical modeling revealed details about how plants switch their epigenetic states. The model predicted a bistable pattern of FLC expression in individual cells. And that’s what they found experimentally with FLC reporter assays.
Unlike us humans, flowering plants can easily remember last winter—they can just look at their epigenetic mods.