Epigenetics – The Molecular Tool in Understanding Abiotic Stress Response in Plants

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factors involved in stress response or to elucidate the molecular circuit

which they regulate. Understanding how epigenetic regulators are engaged

to particular locations in chromatin to perform their function is among the

several intriguing features of studying the molecular process involved in

the triggering the stress response in plants. The recruitment of epigenetic

regulators to specific chromatin regions has been proposed by utilizing: (i)

transcription factor (TF) mediated; (ii) long noncoding RNA-mediated; and

(iii) self-targeting models (Deng et al., 2018). Recruiters involved in stress

response were classified to a TF-mediated model in abiotic stress response.

For instance, in rice (Oryza sativa) indeterminate spikelet 1 (IDS1) has been

recognized as HDAC recruiter and in Arabidopsis, MYB96 is identified as

the same in case of drought stress (Cheng et al., 2018; Lee & Seo, 2019).

During the last few decades, we have gathered more information about the

interactions of a variety of epigenetic components found in chromatin, this

has improved the knowledge of epigenetic control over abiotic stress. Stress

acclimatization can be facilitated by activating or inhibiting gene expression

(Tan et al., 2014; Ueda & Seki, 2020; Zhao et al., 2019).

The methylation of histone molecules is limited to lysine and arginine

residues at various locations on the molecule (H3, H4). Histone methyltrans­

ferase (HMT) consists of histone lysine methyltransferases (HKMTs) and

protein arginine methyltransferases, which are responsible for the transfer

of methyl to histone (PRMTs) (Liu et al., 2010; Zhao et al., 2019). Besides

HTM families, SAM is also a donor of a methyl group to histone for Histone

methylation. Histone methylation is classified into three groups: mono-,

di-, and tri-methylation based on the number of methyl groups that occur

over histone molecules. The various changes that occur on histones have a

distinct impact on gene expression (Liu et al., 2010; Zhao et al., 2019). In

A. thaliana trimethylation of Lys 27 (H3K27me3) suppresses gene expres­

sion while H3K4me3 increases gene transcription (Berr et al., 2011; Zheng

& Chen, 2011). Histone demethylases (HDMs) are enzymes that remove

methyl groups from histones. HDMs are divided into two categories in

plants: (i) lysine-specific demethylase 1 (LSD1); and (ii) Jumonji C domain-

containing proteins (JMJs) (Peng et al., 2017; Shi et al., 2004). In the case of

the two enzymes, the mechanism for demethylation of histone is distinct, as

are the cofactors they utilize. JMJs belong to the 2-oxoglutarate-dependent

dioxygenase family; on the other hand, LSD1 belongs to the flavin-dependent

amine oxidase family (Liu et al., 2010; Xiao et al., 2016). Histone acetyla­

tion is a covalent alteration of histone molecules that involves the transfer

of acetyl groups (CH3COO^–) from acetyl CoA to the ε-amino group of the