Heat can erase epigenetic marks of vernalization in Arabidopsis

Vernalization establishes a memory of winter that must be maintained for weeks or months in order to promote flowering the following spring. The stability of the vernalized state varies among plant species and depends on the duration of cold exposure. In <i>Arabidopsis thaliana</i>, winter leads to epigenetic silencing of the floral repressor gene <i>FLOWERING LOCUS C</i> (<i>FLC</i>) and the duration of cold is measured through the dynamics of chromatin modifications during and after cold. The growing conditions encountered post-vernalization are thus critical for the maintenance of the vernalized state. We reported that high temperature leads to devernalization and, consistently, to <i>FLC</i> reactivation in <i>Arabidopsis</i> seedlings. Here we show that the repressive epigenetic mark H3K27me3 decreases at the <i>FLC</i> locus when vernalized seedlings are grown at 30°C, unless they were first exposed to a stabilizing period at 20°C. Ambient temperature thus controls the epigenetic memory of winter.