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Small RNAs – The Big Players in Developing Salt-Resistant Plants

out by transcriptional machinery in collaboration with a complex system

of transcription factors (Agarwal et al., 2013). Alarming data have shown

salt stress potentially regulates numerous plant genes both at transcriptional

and post-transcriptional levels in different species, underscoring the role of

usual transcriptional regulators during stress (Deinlein et al., 2014; Golldack

et al., 2011). Manipulation of such transcription factors and transcription

system plants showed many adaptive features such as overexpression of

the stress-responsive gene, activity of several transporters, biogenesis of

various protective metabolic substances such as osmolytes, polyamines,

antioxidative enzymes, etc. (Hasegawa, 2013; Yadav et al., 2012). Different

kinds of post-transcriptional and post-translational modifications such as

sumoylation, ubiquitination, etc., also perform a very important role in the

control of gene expression during stressful situations and collectively such

strategies help plants to achieve adaptive modification as well as capability

of survival under salinity (Chen & Aravin, 2015).

9.3 SMALL RNA AND ITS TYPIFICATION

Over a long period, RNA was thought to be a transitional component that

serves as a bridge between gene loci in DNA and polypeptides (mRNAs)

or to be a molecule which is serving effective roles during gene splicing

(snRNA) or to be the components of protein-synthesizing machinery

(t-RNA and rRNA). The subsequent invention of many non-coding small

RNA molecules with distinct regulatory roles has modified the overall

concept regarding gene regulations and gene expressions. sRNAs are 18–30

nucleotides in length and have a large effect on several metabolic regulations

including plant defense responses. Categorization of small RNAs is quite

difficult because of their biogenesis, polarity, and extraordinary differences

in transcript length and based on these criteria sRNA is generally sub­

categorized into two distinct groups: miRNA or microRNA and siRNA or

short interfering RNAs; however, they are often subcategorized into several

other forms. Biochemical and functional properties of both subcategories are

nearly identical, and both of these are 19–20 nt long with 5’-phosphate and

3’-hydroxyl end and in both cases mode of action to silent gene expression

is involved RNA-induced silencing complex (RISC) (Ambros et al., 2003;

Kim, 2005a). After the discovery of plant small RNA (sRNA) in Arabidopsis

in 2002, molecular biologists of various corners of the globe engaged to

invent small RNAs from the various organism and their cumulative effort

explored not only the numerous sRNAs but also determined their mode of