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

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a plethora of signaling pathways that eventually leading to transcriptional

reprogramming (Bhadouriya et al., 2020). This transcriptional reprogram­

ming brings a global change in the expression of genes by various transcrip­

tion factors. During this re-programming, the expressions of specific genes

are exalted while alternative genes get suppressed in comparison to earlier

states. Keeping the genomic sequence unchanged a new molecular charac­

teristic appears which is different from its original form, it also acquires an

entirely new molecular sign, which is heritable, this process is known as

epigenetic reprogramming (Weinhold, 2006). During the last decades, the

basic pathways of stress signaling have been deciphered successively (Zhu,

2016). Several studies have explained the mechanisms of signal transduc­

tion involved under plant abiotic stress, of which numerous studies show

significant involvement of epigenetic mechanism (Kim et al., 2015; Sahu

et al., 2013). The British developmental biologist Conard H. Waddington

coined the word “Epigenetics” by joining two words “epigenesis” and

“genetics.” Epigenetics is the branch of science that deals with genetically

determined characteristics of organisms that are not linked to modifications

in DNA nucleotide sequence but can be effectively imprinted within genome

(Deans & Maggert, 2015). In other words, epigenetic relates to chemical

changes that are both transient and heritable and are not connected with

alterations in DNA sequence (Bird, 2007). Over the past decade, the revolu­

tion in biological science in the field of molecular epigenetics established

it as the “next big thing” (Ebrahim, 2012). The term “Epigenetics” literally

denotes “above or on top of genetics” like “events above or outside the gene”

(Jablonka & Lamb, 2002). Epigenetic changes occurring on chromosomes

include histone modification, DNA methylation, and sRNA-based mecha­

nisms are considered the “three pillars of epigenetics,” they regulate gene

expression (Avramova, 2011; Grant-Downton & Dickinson, 2005). The

epigenetic control of a plant genome is a complex phenomenon in which a

particular group of genes is expressed in response to a specific environmental

and developmental situation (Pikaard & Scheid, 2014). Plants employ three

types of epigenetic processes to acclimate and sustain in harsh environments:

histone modification, DNA methylation, and RNA interference (RNAi)

(Singroha & Sharma, 2019). The productivity of crop is hampered due to

unfavorable environmental factors. In fact, in the case of numerous major

crops there is a reduction in the yield and increase in subsequent price (Lobell

& Gourdji, 2012; Lobell et al., 2011; Moore & Lobell, 2015). In response to

biotic and abiotic environmental stressors, plants alter their growth pattern

as well as physiological processes, to acclimate in the constantly changing