Abstract
The Polycomb Group (PcG) pathway represses transcription through a mechanism conserved among plants and animals. PcG-mediated repression can determine spatial territories of gene expression, but it remains unclear whether PcG-mediated repression is a regulatory requirement for all targets. Here, we show the role of PcG proteins in the spatial regulation of FLOWERING LOCUS T (FT), a main activator of flowering in Arabidopsis thaliana exclusively expressed in the vasculature. Strikingly, the loss of PcG repression causes down-regulation of FT. In addition, our results show how the effect of PcG-mediated regulation differs for target genes and that, for FT expression, it relies primarily on tissue differentiation.
Highlights
Two main complexes are involved in the repression mediated by the Polycomb Group (PcG) pathway
We show that the loss of PcG repression differentially affects targets, and that the domain of FLOWERING LOCUS T (FT) expression depends on tissue differentiation, even in the absence of a PcG-mediated chromatin configuration
FT Expression Is Strongly Reduced in the swn-7 clf-28 PcG Mutant
Summary
Two main complexes are involved in the repression mediated by the Polycomb Group (PcG) pathway. Polycomb Repressive Complex (PRC2) tri-methylates lysine 27 of histone 3 (H3K27me3) and recruits PRC1, which further contributes to the repression of target genes (Hennig and Derkacheva, 2009; Simon and Kingston, 2009). The expression of homeotic (Hox) genes is the paradigm of PcG regulation in animals. Hox genes are expressed only in specific regions of the animal body; in PcG mutants their expression extends to other regions, causing homeotic changes in body patterning (Simon and Kingston, 2009). The best known example of a Hox gene spatially regulated by PcG proteins is the Arabidopsis thaliana MADS box gene AGAMOUS (AG). H3K27me target genes in Arabidopsis often show marked tissue-specific expression patterns (Turck et al, 2007; Zhang et al, 2007). Changes in H3K27me levels are not always
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