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

of 22 nt siRNAs lead translational slowdown and growth inhibition under

certain stress conditions. However, the mechanism of 22 nt siRNAs in the

execution of translational repression and transitive RNA interference are

still under research that mediate translational repression and transitive RNA

interference are still under research.

9.4 OTHER TYPES OF SMALL RNA

In addition to these sRNAs, several classes of small RNAs have been

discovered. Some of them are well studied and found to have significant

involvement in diverse cellular processes of animals and fungi. Such sRNAs

are functionally diverse with scanty information. To date, there is no report

about the occurrence of such small RNAs in plant species, but they have

pivotal roles in the gene regulation of a few biological phenomena in some

members of the animal kingdom (Jones-Rhoades et al., 2006). From a

botanical perspective, miRNAs and siRNAs make up an entire portion of the

sRNA population.

9.4.1 SMALL TEMPORAL RNA (ST-RNA)

In C. elegans, a specialized group of 22 nt long RNAs have been reported

that are known as Small Temporal RNA (st-RNA) and are involved in

temporal regulation of the developmental process of the organism (Thakur,

2003). Further studies revealed that initially, these are generated from ~

70-nt ssRNA having a stem-loop structure and after processing, this st-RNA

is thought to prevent their target mRNA by binding with the target comple­

mentary 3’ untranslated regions (Thakur, 2003).

9.4.2 PIWI-INTERACTING RNA (PI-RNA)

Piwi-interacting RNAs (piRNAs) are another type of small RNA that

is frequently regarded as a distinct class of miRNAs with a length range

between 24 and 32 nucleotides and are mostly expressed in germline cells

of some animals (Aravin et al., 2007). These pi-RNAs act as a vital genetic

and epigenetic regulatory factor and effectively regulate the stability of germ

cells, genome integrity, stability of mRNA, methylation of DNA and control

of retrotransposons (Zuo et al., 2016).