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DNA replication–coupled histone modification maintains Polycomb gene silencing in plants

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Science  15 Sep 2017:
Vol. 357, Issue 6356, pp. 1146-1149
DOI: 10.1126/science.aan4965

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Managing gene silencing through replication

Vernalization is the process in plants by which wintertime chill stimulates springtime flowering. Yang et al. and Jiang and Berger show how chill is recorded in Arabidopsis epigenetically by methylation of histones. Specialized components of the Polycomb group of proteins remodel DNA to establish the methylation marks and are linked to DNA replication. Long-term stable epigenetic status follows rapid establishment of metastable epigenetic marks. This epigenetic strategy may be key to the developmental requirement of both secure and nimble fate decisions, allowing plant cells to change fates.

Science, this issue p. 1142 and p. 1146

Abstract

Propagation of patterns of gene expression through the cell cycle requires prompt restoration of epigenetic marks after the twofold dilution caused by DNA replication. Here we show that the transcriptional repressive mark H3K27me3 (histone H3 lysine 27 trimethylation) is restored in replicating plant cells through DNA replication–coupled modification of histone variant H3.1. Plants evolved a mechanism for efficient K27 trimethylation on H3.1, which is essential for inheritance of the silencing memory from mother to daughter cells. We illustrate how this mechanism establishes H3K27me3-mediated silencing during the developmental transition to flowering. Our study reveals a mechanism responsible for transmission of H3K27me3 in plant cells through cell divisions, enabling H3K27me3 to function as an epigenetic mark.

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