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

sRNAs of interest were identified and their targets were also identified.

A correct prediction and effective validation of small RNAs target gene

is highly beneficial to researchers in investigating how these sRNAs may

be used to regulate various plant biological activities. Any sort of stress-

sensitive genes, including salt-tolerance genes are intensively regulated by a

complex system of transcription factors and SRNAs (Devi et al., 2013; Li et

al., 2010, 2012). These miRNAs regulate several essential salt reactive genes

and transcription factors (Table 9.1), and regulators were proven critical to

plant salt tolerance (Fang et al., 2014; Mondal et al., 2018; Woodrow et al.,

2012). Under any stressful condition all the developmental, metabolic, and

adaptive processes in the plant, rely on the proper regulation of gene expres­

sion system, which may be achieved by either transcriptional regulation or

post-transcriptional regulation.

9.6.1 TRANSCRIPTIONAL GENE SILENCING (TGS)

The process of shutting down gene expression at the transcription level is

referred to as transcriptional gene silencing (TGS). Usually, such transcrip­

tional repressions are caused by chromatin modification or methylation of

DNA. TGS in the plant is usually related to sRNA-directed DNA methyla­

tion (Sunkar & Zhu, 2004). Such silence needs the homology of sequences

between the promoter and sRNA, which is thus also called homology-related

gene silence (HDGS) (Kooter et al., 1999). To date, many miRNAs are

reported to act on salt responsive genes and induce DNA methylation (Table

9.1). In some plants, many subsets of hc-siRNAs have been recognized that

are intricately related to DNA methylation and in turn, considered to influ­

ence salt tolerance. In a study, it was found that the capability of salt toler­

ance in Arabidopsis was decreased when the DNA methylation at cytosine

was blocked by the treatment of any agent such as 5-azacytidine (Boyko et

al., 2010).

9.6.2 POST-TRANSCRIPTIONAL GENE SILENCING (PTGS)

Post-transcriptional gene silencing (PTGS) is a process in which transcription

remain unaffected, but the expression of the gene is lost as mRNA molecule

become unstable. sRNAs generally function as sequence determinants for

such gene silencing in plants. Distinct components have interacted during

PTGS and components may differ for miRNA mediated PTGS and siRNA