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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

changes in chromatin structure resulting in either transcriptional repression

or stimulation (Teperino et al., 2010). ADD (ATRX-DNMT3-DNMT3L),

ankyrin, Bromo-adjacent homology, chromo-barrel, chromodomain (CD),

double chromodomain, plant homeodomain (PHD), Pro-Trp-Trp-Pro

(PWWP), SAWADEE, Tudor, WD40, and zinc finger CW have all been

observed to detect either unmethylated and methylated Lys or Arg moiety

therefore act as “readers” (Allis & Jenuwein, 2016; Andrews et al., 2016;

Bannister & Kouzarides, 2011; Taverna et al., 2007; Xu et al., 2017). The

reader proteins mentioned seems to have largely stable across a wide range

of eukaryotic species; nevertheless, in Arabidopsis, a single Tudor domain of

the EMSY-LIKE1 H3K4me2/3 reader protein have been discovered (Zhao

et al., 2018). Monoubiquitination of H2A (H2Aub) and H2B (H2Bub) are

involved in both an operative as well as suppressive signal in eukaryotic

transcription. Arabidopsis H2AK121 monoubiquitination (H2AK121ub)

co-localizes with H3K27me3 autonomously and never collaboratively with

POLYCOMB REPRESSIVE COMPLEX2 (PRC2) a protein that is required

for the maintenance of H3K27me3. The function of Polycomb Group

(PcG) controls the accessibility of chromatin. At transcriptional regulatory

hotspots, H2AK121ub is connected to a less accessible and yet permissive

chromatin. Regardless of the fact that the reduction of PcG activity increases

chromatin accessibility, this is not always followed by transcriptional activa­

tion, suggesting that accessible chromatin is not always a predictor of gene

expression (Bratzel et al., 2010; Yin et al., 2021; Zhou et al., 2017). For DNA

methylation and heterochromatic histone H3 methylation, deubiquitination

of H2B is essential (Sridhar et al., 2007). H2B monoubiquitination particu­

larly stimulates transcription by the accumulation of H3K4me3 (Geng et al.,

2012). During the last three decades, multiple studies found turnover rates

from fast (few minutes) to sluggish across four core histones, identified in

yeast (Saccharomyces cerevisiae) to multicellular plants (Waterborg, 2002;

Zheng et al., 2013). Due to their longer half-life, methylation may have a

benefit of prolonged response, while seen in flowering and the inheritance of

transgenerational stress memory (priming). Several research demonstrated

numerous epigenetic regulators for acetylation that are involved in the abiotic

stress response (Asensi-Fabado et al., 2017; Luo et al., 2017). Histone or/

and DNA methylation along with other PTMs like Ser-5P RNAPolII act

as epigenetic regulation of prolonged responses like blossoming, stress

memory (Ding et al., 2012). Since these epigenetic changes are variable,

readers, writers, and erasers must collaborate (Xu et al., 2017). To completely

comprehend epigenetic regulation, it is necessary to identify the epigenetic