Hydrolase that can remove conjugated ubiquitin from proteins in vitro and may therefore play an important regulatory role at the level of protein turnover by preventing degradation (PubMed:21690391, PubMed:24659992). Binds chromatin (e.g. nucleosomes and histones) and has enzymatic histone deubiquitinase activity, specific for the H2B histone (PubMed:21690391, PubMed:28703681). Can both repress (e.g. OSR2) and promote (e.g. AN3) the expression of target genes by associating with chromatin, deubiquitinating H2B and regulating its euchromatic histone marks (e.g. H3ac and H3K4me) (PubMed:28703681). In association with LDL1/KDM1C, involved in transcriptional gene repression via histone deubiquitination and demethylation (PubMed:21690391). Promotes the concerted epigenetic regulation and repression (e.g. the removal of euchromatic histone acetylation, ubiquitination, and methylation marks) of a set of genes (e.g. GA20OX, WUS, OSR2, ARL and ABI5) that collectively limit plant growth thus stimulating plant growth and increasing cell size (PubMed:27999174). Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). Interacts with KDM1C. Mostly expressed in stems flowers and siliques, and, to a lower extent, in leaves, roots and seedlings. Up-regulated expression of GLP2A/GLP5A due to derepression associated with H2B hyperubiquitination of the target chromatin and H3K4 hypermethylation (PubMed:21690391). Abnormal hallmarks of euchromatin including H3 hyperacetylation, H2B monoubiquitination and H3K4 trimethylation in the gene encoding OSR2 leading to its increased expression (PubMed:27999174). Repressed expression of the AN3 gene associated with epigenetic modification (e.g. H2B hyperubiquitination and reduced H3ac and H3K4me) of its chromatin (PubMed:28703681). Belongs to the peptidase C85 family.