Histone modifications during the life cycle of the brown alga Ectocarpus

Simon Bourdareau,Leila Tirichine,Susana M Coelho,Yue Wu,J Mark Cock,Delphine Scornet,Damarys Loew,Bérangère Lombard

doi:10.1186/s13059-020-02216-8

Abstract

BackgroundBrown 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 expected to provide important insights into the evolutionary events necessary for the emergence of complex multicellularity. Here, we focus on mechanisms of epigenetic regulation involving post-translational modifications of histone proteins.ResultsA total of 47 histone post-translational modifications are identified, including a novel mark H2AZR38me1, but Ectocarpus lacks both H3K27me3 and the major polycomb complexes. ChIP-seq identifies modifications associated with transcription start sites and gene bodies of active genes and with transposons. H3K79me2 exhibits an unusual pattern, often marking large genomic regions spanning several genes. Transcription start sites of closely spaced, divergently transcribed gene pairs share a common nucleosome-depleted region and exhibit shared histone modification peaks. Overall, patterns of histone modifications are stable through the life cycle. Analysis of histone modifications at generation-biased genes identifies a correlation between the presence of specific chromatin marks and the level of gene expression.ConclusionsThe overview of histone post-translational modifications in the brown alga presented here will provide a foundation for future studies aimed at understanding the role of chromatin modifications in the regulation of brown algal genomes.

Highlights

Very few eukaryotic lineages have independently evolved complex multicellularity, and the brown algae are of particular interest as the third most developmentally complex lineage after animals and land plants
Most of the acetyltransferases were sufficiently similar to well-characterised homologues to allow prediction of their target residues, but the methyltransferases tended to be less conserved at the sequence level and, in many cases, had novel domain structures
For example based on mutant analysis, will be necessary to investigate the specificity of the Ectocarpus methyltransferases

Summary

Introduction

Very few eukaryotic lineages have independently evolved complex multicellularity, and the brown algae are of particular interest as the third most developmentally complex lineage after animals and land plants. Histones have been shown to undergo a broad range of different post-translational modifications (PTMs) involving the addition of various chemical moieties to multiple amino acid residues, within the unstructured amino-terminal “tails” of these proteins [1]. These modifications affect chromatin function either by directly modifying interactions between the different components of the nucleosome or via the action of proteins that bind to specific histone modifications and effect specific tasks. We focus on mechanisms of epigenetic regulation involving post-translational modifications of histone proteins

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