Evidence That Local Chromatin Holds the Memory for Epigenetic Inheritance of Gene Expression; Polycomb Repressive Complex Plays Key Role; Arabidopsis Epigenetically “Remembers” When to Flower After Exposure to Cold

New research findings by John Innes Centre (JIC) scientists in the UK have helped to settle an important debate in the field of epigenetic inheritance. Using the flowering plant Arabidopsis thaliana as a model for their research, Professor Martin Howard, Professor Caroline Dean, and members of their labs, have been trying to understand how organisms “remember” past events at the cellular level. Previous work had shown that expression of a gene called FLC (the flowering locus C gene), which serves as a “brake” to stop plants flowering until after winter, is repressed by exposure to cold. Furthermore, the amount of repression is epigenetically “remembered” after winter to permit flowering at the appropriate time. In many organisms, DNA is packaged around histone proteins to make a structure called chromatin. Intriguingly, the level of FLC repression is correlated with the level of cold-induced chemical modifications to the histones at the FLC gene, added by a protein complex called Polycomb Repressive Complex 2. But are these histone modifications or other local features of the chromatin the cause of epigenetic memory, or are they a consequence of memory stored elsewhere? The findings of a new study, published online on May 8, 2015 in the open-access journal eLife, provide compelling evidence that has helped to settle this long-standing debate of where this memory is stored. The eLife article is titled “Local Chromatin Environment of a Polycomb Target Gene Instructs Its Own Epigenetic Inheritance.” Professor Howard explains: "We engineered plant cells to contain two distinguishable copies of FLC. When one copy of the gene is expressed, it generates a protein that glows red; when the other copy is expressed a yellow fluorescent protein is made.
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