Abstract
Background Brown algae evolved complex multicellularity independently of the animal and land plant lineages and are the third most developmentally complex phylogenetic group on the planet. An understanding of developmental processes in this group is expect to provide important insights into the evolutionary events necessary for the emergence of complex multicellularity. Here we have focused on mechanisms of epigenetic regulation involving post-translational modifications (PTMs) of histone proteins.
Results A total of 45 histone PTMs were identified, including two novel marks, but Ectocarpus lacks both H3K27me3 and the major polycomb complexes. ChIP-seq identified PTMs associated with transcription start sites (TSSs) and gene bodies of active genes, and with transposons. H3K79me2 exhibited an unusual pattern, often marking large genomic regions spanning several genes. TSSs of closely spaced divergently transcribed gene pairs shared a common nucleosome depleted region and exhibited shared histone PTM peaks. Overall, patterns of histone PTMs were stable through the life cycle. Analysis of histone PTMs at generation-biased genes provided insights into their functions during gene induction.
Conclusions The overview of the nature and functions of histone PTMs in the brown algae presented here will provide a foundation for future studies aimed at understanding epigenetic processes in the brown algae.