Introduction Histone is the core component
Histone is the core component of chromatin and histone modification is one of the key mechanisms of epigenetic regulation (Bannister and Kouzarides, 2011). Amino p-selectin residues on histone tails can be modified under different mechanisms including acetylation, methylation, phosphorylation, ubiquitination or ADP-ribosylation (Greer and Shi, 2012). Histone acetylation and deacetylation play pivotal roles in the regulation of gene expression via altering chromatin status, and they are conducted by two types of enzymes: histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively. Histone acetylation mediated by HATs is generally associated with gene up-regulation, while histone deacetylation catalyzed by HDACs is correlated to repressive gene expression (Chen and Tian, 2007).
So far, the genome wide identifications of HATs and HDACs have been achieved in several model plant species, like Arabidopsis thaliana and Oryza sativa. In plants, HATs are classified into four families: GNAT (the general control non-repressible 5-related N-terminal acetyltransferase) family, MYST (the MOZ, Ybf2/Sas3, Sas2, and Tip60) family, CBP (the p300/CREB (cAMP-responsive element-binding protein)-binding protein) family as well as TAFII250 (the TATA-binding protein-associated factor) family (Pandey et al., 2002). Increasing evidence shows that HATs contribute to many aspects of plant growth and developmental process. AtHAC1 and AtGCN5 (AtHAG1) have been proved to control the flowering time. AtGCN5 (AtHAG1) along with AtTAF1 (HAF1) were found to be involved in root development and regulating the expression of light inducible genes (Benhamed et al., 2006; Kornet and Scheres, 2009). Moreover, AtMYSTs and AtELP3 (HAG) are characterized as the regulator of gametophyte development (Latrasse et al., 2008) and cell proliferation (Fina and Casati, 2015), respectively.
In plants, histone deacetylation is catalyzed by three HDAC family proteins: RPD3 (the yeast reduced potassium dependency 3)/HDA1 superfamily, SIR2 (silent information regulator 2) family and HD2 (type 2 histone deacetylases). Previous study shows that the function of SIR2 family proteins is tightly linked to the auxin synthesis and transport pathways (Grozinger et al., 2001). In addition, the development of vascular tissues, hypocotyls as well as the root system in Arabidopsis were repressed upon treatment with sirtinol (the inhibitor of sirtuin proteins). HD2 proteins (AtHD2A, AtHD2B and AtHD2C) have key roles in the seed developmental process (Colville et al., 2011). AtHD2A and AtHD2B also contribute to the establishment of leaf polarity (Ueno et al., 2007) as well as integration of transfer DNA in the process of Agrobacterium mediated transformation (Crane and Gelvin, 2007). Additionally, AtHD2C has been proven to be involved in ABA modulation as well as stress response (Wu et al., 2000). As the symbol of RPD3/HDA1 superfamily, AtHDA19 (AtRPD3A) and AtHDA6 (AtRPD3B) are the most well-studied histone deacetylases in plants. AtHDA19 is highly expressed in all tissues and has an essential role in globally gene expression regulation (Alinsug et al., 2009). AtHDA19 was also found to regulate plants’ adaptation to abiotic stresses and defense against pathogens (Zhou et al., 2005). While AtHDA6 has a preference of repression of repetitive transgenic and endogenous genes (Alinsug et al., 2009).
Marchantia polymorpha, the liverworts, is one of three lineages of bryophytes and becomes a newly emerging model plants because of its basal and critical phylogenetic position (Shimamura, 2015). The complete genome sequence of Marchantia was released by Bowman et al. (2017). Along with the improved genetic modifying tools, it provides an opportunity to perform molecular study in Marchantia, and further dissect the mechanism of acetylation-based histone modification, which has never been addressed in lower land plants before (Chiyoda et al., 2008; Kubota et al., 2013).