The histone deubiquitinase OTLD1 targets euchromatin to regulate plant growth

Histone monoubiquitination is associated with active chromatin and plays an important role in epigenetic regulation of gene expression in plants. Deubiquitinating enzymes remove the ubiquitin group from histones and thereby contribute to gene repression. The Arabidopsis thaliana genome encodes 50 deubiquitinases, yet only 2 of them - UBP26 and OTLD1, members of the USP/UBP (ubiquitin-specific protease and ubiquitin-binding protein) and OTU (ovarian tumor protease) deubiquitinase families - are known to target histones. Furthermore, UBP26 is the only plant histone deubiquitinase for which the functional role has been characterized in detail. We used gain-and loss-of-function alleles of OTLD1 to examine its role in the plant life cycle and showed that OTLD1 stimulates plant growth, increases cell size, and induces transcriptional repression of five major regulators of plant organ growth and development: GA20OX, WUS, OSR2, ARL, and ABI5. OTLD1 associated with chromatin at each of these target genes and promoted the removal of euchromatic histone acetylation, ubiquitination, and methylation marks. Thus, these data indicate that OTLD1 promotes the concerted epigenetic regulation of a set of genes that collectively limit plant growth.