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

lysine. As a result of this change, the (+) charge on lysine is neutralized,

the connection across the altered histone as well as DNA is weakened,

allowing the chromatin to unfold (Marmorstein & Zhou, 2014; Zhao et

al., 2019). Acetylated histones may engage different proteins that are able

to alter chromatin structure (Nie et al., 2019; Zhang et al., 2016). Histone

hyperacetylation enhances transcriptional upregulation, and hypoacetylation

promotes gene suppression (Marmorstein & Zhou, 2014; Zhang et al., 2016;

Zhao et al., 2019). HATs and HDACs have opposing activities that govern

histone acetylation levels (Pandey et al., 2002; Pikaard & Scheid, 2014).

Plant HATs are classified in four groups: (i) p300/CREB (cAMP-responsive

element-binding protein)-binding proteins (CBP); (ii) TATA-binding

protein-associated factors (TAF1); (iii) (GNAT) GCN5-related N-terminal

acetyltransferases; (iv) MYST (MOZ, Ybf2/Sas3, Sas2, and Tip60-related

proteins) (Pandey et al., 2002). HDACs are important epigenetic regulators

that suppress gene expression in a range of cellular activities such as plant

growth, development, and stress response. Plant’s HDACs may be classified

into three families: (a) reduced potassium dependency 3/histone deacetylase

1 (RDP3/HDA1); (b) silent information regulator 2 (SIR2); and (c) plant-

specific histone deacetylase 2 (PSHDA2) (Yang et al., 2018). The HDACs

employ different cofactors: the catalytic domain of SIR2 (sirtuins) proteins

requires nicotine adenine dinucleotide (NAD⁺) as a cofactor; whereas the

RPD3/HDA1 family need a Zn²⁺ cofactor to deacetylate and the HD2 family

proteins are zinc-dependent HDACs since they have a conserved pentapep­

tide motif (MEFWG) at their N-terminus (Lee & Cho, 2016; RM et al., 2020;

Seto & Yoshida, 2014).

12.4.3 NON-CODING RNAS

sRNAs are non-coding RNAs (ncRNAs) with 20–24 nt that are contemporary

in the field of epigenetic control. They are small weapons (bio-regulators)

that protect plants against diverse stress. ncRNAs are key epigenetic regu­

lators in plants that regulate a variety of cellular activities, like growth,

development, or even respond to abiotic stress. ncRNAs are classified into

different types depending on their length: (i) non-coding RNAs with a short

chain; and (ii) non-coding RNAs with a long chain (Brant & Budak, 2018;

Hou et al., 2019; Wang et al., 2017). Several short chain ncRNAs consisting

of miRNAs and siRNAs were documented over the years with a role in both

transcriptional and post-transcriptional gene regulation in animals and plants