The cis-regulatory code that underpins the regulation of eukaryotic genes is strongly dependent on local chromatin structure. While an open chromatin structure facilitates the access of regulatory factors to their cognate binding sites, a particularly repressive structure, as found in chromatin regions targeted by the repressive Polycomb Group (PcG)-pathway, silences potential cis-regulatory regions by preventing the access of transcription factors.
Genes with a key regulatory role in plant development are often subject of PcG-mediated repression, which contributes to the strict spatio-temporal control of these key genes. We are now beginning to understand how genes become PcG targets in the first place. Our group recently discovered that transcription factors belonging to the TELOMERE REPEAT BINDING PROTEIN (TRB) family are involved in recruiting PcG complexes to a subset of their target genes. Furthermore, our recent data indicate that the hierarchical “text book knowledge” of a strictly ordered PcG subcomplex recruitment is in dire need of replacement by a more flexible model, in which different PcG complex variants, which are highly connected through protein-protein interactions, may be targeted through distinct transcription factor families. These new insights explain in part, why cis-regulatory elements that define PcG target gene status have eluded discovery in the past.