H3K27me1 is E(z) in animals, but not in plants.

Post-translational modifications of histones play key roles in the regulation of gene expression and chromatin structure in eukaryotes. Methylation of histone 3 on lysine 27 (H3K27) is one of the most common and well-studied histone modifications. The vast majority of research on this histone residue, however, has focused on the trimethylated form (H3K27me3). Despite occurring at higher levels than H3K27me3 in animals and plants, the monomethylated form of H3K27 (H3K27me1) remains relatively poorly characterized. The absence of information concerning H3K27me1 is due in large part to the fact that the enzymes catalyzing this epigenetic mark were only recently identified. In this article, we highlight new findings concerning H3K27me1, including the identification of two plant-specific H3K27 monomethyltransferases that are required for gene silencing and heterochromatin condensation. We also discuss the emerging similarities and differences in H3K27 methylation in plant and animal systems.