Histone modifications like acetylation, methylation, phosphorylation which determines DNA accessibility by transcription factors and coregulators plays a significant role in gene regulation. Lysine at the N-terminal tail of core histones are acetylation and methylation dominant sites. Hyperacetylation of histone lysine results in transcription activation as a result of chromatin relaxation, whereas hypoacetylation causes chromatin compaction leading to gene repression.

General control non-repressible 5 (GcN5)-related N-acetyltransferases (GNAT) belongs to histone acetyltransferase (HAT) family of proteins, which catalyze the transfer of acetyl group from acetyl CoA to the amine moiety on acceptor molecules.  The GNAT family comprises three subfamilies namely GcN5, ELP3 (transcriptional elongator complex protein) and HAT1 (Pandey et al., 2002). Arabidopsis genome comprises single homolog of each of these subfamilies- GcN5 (HAG1/AtGcN5), ELP3 (HAG3) and HAT1 (HAG2) and are characterized by presence of HAT domain (Pandey et al., 2002) comprising of A-D motifs (Sterner and Berger., 2000) along with other domains like bromodomain in HAG1 and radical S-adenosylmethionine-binding domain in HAG3 (Fina and Casati., 2015). These enzymes acetylate different lysine residues on histone, HAG1 acetylates H3K14 and HAG2 acetylates H4K12. Arabidopsis HAG3 participates in UV-B responses directly or indirectly since hag3 RNA interference (RNAi) transgenic plants showed higher levels of UV-B absorbing compounds with reduced UV-B induced DNA damage and lower growth inhibition in leaf and root region as compared to wild type plants. However, hag1 and hag2 RNAi transgenic plants did not show any significant differences as compared to wild type plants (Fina and Casati., 2015). GNATs from barley, Hordeum vulgare L. consist of HvMYST, HvELP3 and HvGCN5. These genes are induced by phytohormone abscisic acid (ABA) and  involved in seed development due to their quantitative differences during seed development stages and difference in seed parameters like weight and size among different cultivars (Papaefthimiou et al., 2010). From transcriptome data analysis of barley in response to biotic stress and hormonal treatment, members of the GNAT family were significantly upregulated in response to biotic stress and downregulated in response to hormonal treatments. Also major members of GNAT, NF-YC and WHIRLY were among top regulators classes and were considered as hub genes (Soltani et al., 2023)

Last updated June 2023 by Ankita Abnave

References:

Fina JP, Casati P. HAG3, a Histone Acetyltransferase, Affects UV-B Responses by Negatively Regulating the Expression of DNA Repair Enzymes and Sunscreen Content in Arabidopsis thaliana. Plant Cell Physiol. 2015 Jul;56(7):1388-400. doi: 10.1093/pcp/pcv054. Epub 2015 Apr 22. PMID: 25907565.

Pandey R, Müller A, Napoli CA, Selinger DA, Pikaard CS, Richards EJ, Bender J, Mount DW, Jorgensen RA. Analysis of histone acetyltransferase and histone deacetylase families of Arabidopsis thaliana suggests functional diversification of chromatin modification among multicellular eukaryotes. Nucleic Acids Res. 2002 Dec 1;30(23):5036-55. doi: 10.1093/nar/gkf660. PMID: 12466527; PMCID: PMC137973.

Sterner DE, Berger SL. Acetylation of histones and transcription-related factors. Microbiol Mol Biol Rev. 2000 Jun;64(2):435-59. doi: 10.1128/MMBR.64.2.435-459.2000. PMID: 10839822; PMCID: PMC98999.

Soltani Z, Moghadam A, Tahmasebi A, Niazi A. Integrative systems biology analysis of barley transcriptome ─ hormonal signaling against biotic stress. PLoS One. 2023 Apr 27;18(4):e0281470. doi: 10.1371/journal.pone.0281470. PMID: 37104505; PMCID: PMC10138258.

Papaefthimiou D, Likotrafiti E, Kapazoglou A, Bladenopoulos K, Tsaftaris A. Epigenetic chromatin modifiers in barley: III. Isolation and characterization of the barley GNAT-MYST family of histone acetyltransferases and responses to exogenous ABA. Plant Physiol Biochem. 2010 Feb-Mar;48(2-3):98-107. doi: 10.1016/j.plaphy.2010.01.002. Epub 2010 Jan 15. PMID: 20117010.