Responsible for the deacetylation of lysine residues on the N-terminal part of the core histones (H2A, H2B, H3 and H4) (Probable). Histone deacetylation gives a tag for epigenetic repression and plays an important role in transcriptional regulation, cell cycle progression and developmental events (Probable). Histone deacetylases act via the formation of large multiprotein complexes (PubMed:25922987). Involved in the regulation of flowering time by repressing FLC and AGL27/MAF1 expression (PubMed:25922987). Forms a histone deacetylase complex with HDA6, FLD and MSI4/FVE that represses FLC gene expression to control flowering time (PubMed:25922987). Unlike its tandem duplication HDA18, HDA5 does not seem to be required for the cellular patterning in the root epidermis (PubMed:16176989). H2O + N(6)-acetyl-L-lysyl-[histone] = acetate + L-lysyl-[histone] Binds 1 zinc ion per subunit. Inhibited by trichostatin A (TSA), a well-known histone deacetylase inhibitor. Interacts with HDA6. A number of isoforms are produced. According to EST sequences. Expressed in stems, leaves, flowers, siliques and mature seeds. Delayed flowering under both long-day (LD) and short-day (SD) conditions. Belongs to the histone deacetylase family. HD type 2 subfamily.