Monoubiquitination of histone H2A and H2B: News and views

Fine-tuning eukaryotic gene expression heavily relies on chromatin regulatory mechanisms involving dynamic exchanges and modifications of histones. Here, we review the main pathways that mediate histone H2A and H2B monoubiquitination and ubiquitination in Arabidopsis thaliana. These histone post-translational modifications are linked to multiple chromatin regulatory layers, enabling distinct functional outcomes across the genome and in response to developmental and environmental signals. Indeed, while H2A ubiquitination primarily attenuates transcription either independently or together with PRC2-mediated H3K27 trimethylation, H2B monoubiquitination facilitates nucleosome dynamics and RNA polymerase II progression during gene activation. Given the widespread role of histone ubiquitination mechanisms in plant development, we also discuss how H2Aub and H2Bub homeostasis influences genome regulation. Finally, by referencing yeast and metazoans, we highlight examples of distinctive plant molecular mechanisms and epigenetic interplays involving histone ubiquitination.