Abstract
Inheritance of gene expression states is fundamental for cells to 'remember' past events, such as environmental or developmental cues. The conserved Polycomb Repressive Complex 2 (PRC2) maintains epigenetic repression of many genes in animals and plants and modifies chromatin at its targets. Histones modified by PRC2 can be inherited through cell division. However, it remains unclear whether this inheritance can direct long-term memory of individual gene expression states (cis memory) or instead if local chromatin states are dictated by the concentrations of diffusible factors (trans memory). By monitoring the expression of two copies of the Arabidopsis Polycomb target gene FLOWERING LOCUS C (FLC) in the same plants, we show that one copy can be repressed while the other is active. Furthermore, this 'mixed' expression state is inherited through many cell divisions as plants develop. These data demonstrate that epigenetic memory of FLC expression is stored not in trans but in cis.
Highlights
Epigenetic memory can be stored in the concentrations of diffusible regulatory factors that are maintained through feedback loops (Novick and Weiner, 1957; Ptashne, 2004; Zacharioudakis et al, 2007 ; Xu et al, 2009)
If FLOWERING LOCUS C (FLC) chromatin states instruct their own inheritance, it should be possible for different copies of FLC within a cell to exist in different heritable transcriptional states
The transgenes consist of 12 kb of genomic DNA surrounding FLC with the Venus or mCherry sequence inserted as a translational fusion into FLC exon 6 (Figure 1A)
Summary
Epigenetic memory can be stored in the concentrations of diffusible regulatory factors that are maintained through feedback loops (trans memory) (Novick and Weiner, 1957; Ptashne, 2004; Zacharioudakis et al, 2007 ; Xu et al, 2009). FLC repression requires PRC2 but is independent of DNA methylation (Finnegan et al, 2005), making it a useful system for studying the cis-memory storage capability of Polycomb at a single gene. Genes and chromosomes | Plant biology number of cells in which FLC is stably repressed increasing quantitatively with the duration of prior cold exposure (Angel et al, 2011).
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