Abstract
Polycomb group (PcG) proteins are essential to maintain gene expression patterns during development. Transcriptional repression by PcG proteins involves trimethylation of H3K27 (H3K27me3) by Polycomb Repressive Complex 2 (PRC2) in animals and plants. PRC1 binds to H3K27me3 and is required for transcriptional repression in animals, but in plants PRC1-like activities have remained elusive. One candidate protein that could be involved in PRC1-like functions in plants is LIKE HETEROCHROMATIN PROTEIN 1 (LHP1), because LHP1 associates with genes marked by H3K27me3 in vivo and has a chromodomain that binds H3K27me3 in vitro. Here, we show that disruption of the chromodomain of Arabidopsis thaliana LHP1 abolishes H3K27me3 recognition, releases gene silencing and causes similar phenotypic alterations as transcriptional lhp1 null mutants. Therefore, binding to H3K27me3 is essential for LHP1 protein function.
Highlights
Polycomb group (PcG) proteins maintain gene expression patterns during development in animals and plants by establishing a cellular memory system for transcriptional repression [1]
An LIKE HETEROCHROMATIN PROTEIN 1 (LHP1) mutant protein with a defective chromodomain The new lhp1-7 allele was discovered in a suppressor screen of a late flowering transgenic line with reduced MSI1 function
The lhp1-7 allele was introduced into the Columbia wild-type by backcrossing, and all further experiments were performed with lhp1-7 in the wild-type background unless otherwise specified
Summary
Polycomb group (PcG) proteins maintain gene expression patterns during development in animals and plants by establishing a cellular memory system for transcriptional repression [1]. Many functional details of PcG proteins remain unknown, current models suggest that repression involves trimethylation of histone H3 lysine 27 (H3K27me3) by Polycomb repressive complex 2 (PRC2). Binding of PRC1 to H3K27me is mediated by the chromodomain of the PRC1 subunit Polycomb (Pc) [3]. Metazoan PRC1 complexes catalyze H2A monoubiquitylation via their RING-domain subunits and are needed for stable repression of PcG target genes [2]. The PcG system is present in plants and PRC2 homologs have similar functions, no clear plant PRC1 homologs have been identified [1]. Proteins that may have PRC1-like functions in plants include EMBRYONIC FLOWER 1, VERNALIZATION 1, LIKE HETEROCHROMATIN PROTEIN 1 (LHP1) and RAWUL-proteins [4,5,6,7]
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