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Varsha Gaitonde Research scholarPG-14042Dept. of Genetics and Plant BreedingIASc, BHU, Varanasi.

SMALL RNA

• Small RNAs of 20–30 nucleotides guide regulatory processes at the DNA or RNA level

• Forms from ds RNA

• Dicer/ Slicers are involved

• Argounots play key role in PTGS

LANDMARKS IN SMALL RNA• 1990 co-suppression of purple color in plants.• 1995 Guo S, and Kemphues KJ. First noticed that sense RNA was as effective as antisense RNA

for suppressing gene expression in worm C. elegans• 1998 Fire et al. First described RNAi phenomenon in C. elegans by injecting dsRNA into C.

elegans which led to an efficient sequence-specific silencing and coined the term "RNA Interference".

• 2000 Zamone et al.Reported processing of long dsRNA by Rnase III (Dicer) into shorter fragments of 21-23-nt intervals in Drosophila extracts

• 2001 Bernstein et al. Cloned Dicer, the RNase III enzyme that is evolutionarily conserved and contains helicase and PAZ domains, as well as two dsRNA-binding domains.

• 2002 Tuschl T and colleagues First described RNAi in mammalian cells• 2003 Paddison et al. Sui et al. Paul et al. Short hairpin RNAs (shRNAs) induce sequence-specific

silencing in mammalian cells.• 2003 Song et al. First reported that siRNAs can be used therapeutically in whole animals• 2004 Kawasaki and Taira Morris et al. First observed that siRNA silences gene at transcriptional

level possibly through directing de novo DNA methylation.• 2006 Nobel Prize in Medicine to Andrew Z. Fire (Stanford University) and to Craig C. Mello

(University of Massachusetts Medical School) for their discovery of RNA interference - gene silencing by double-stranded RNA

• 2007 Smith, L.M., Pontes, O., Searle, I., Yelina, N.E., Yousafzai, F.K., Herr, A.J., Pikaard, C. and Baulcombe, D. A novel SNF2 protein associated with nuclear RNA silencing and spread of a silencing signal between cells in Arabidopsis.

MAJOR FIELDS COVERED1. Improving plant architecture(biomass)2. Yield3. Improving shelf-life of fruits and vegetables4. Delayed ripening5. Enhanced nutritional vale and edibility6. Seedless fruit development (Parthenocarpy)7. Biotic stress resistance-fungus, nematode, bacteria etc. 8. Abiotic- Cold, salinity, drought, heat, oxidative stress,9. Viral resistance10. Nutritional improvement11. Allergin and antinutrition compounds elimination12. Drug development

SMALL RNA• Utilized either for silencing a gene of interest by RNAi or

altering the expression of a gene by over-expressing a miRNA or introduction of artificially synthesized miRNA targeting it.

• Utilized to improve the food productivity (biomass and grain yield) but its nutritional value (cereals, fruits, and vegetables enriched with essential minerals, vitamins, fatty acids, and amino acids).

• Exploited to develop plants with improved resistance against various environmental stresses (especially drought) and biotic stresses like pathogen attack (virus, bacteria, insects, and nema- todes).

• The systemic RNA silencing signal has been identified in plants by direct sampling of phloem sap and detection of RNAs in stocks and scions of grafted plants found in oilseed rape and pumpkins.

ROLE IN CROP IMPROVEMENT

ROLE IN CROP IMPROVEMENT

ROLE IN CROP IMPROVEMENT

ROLE IN CROP IMPROVEMENT

ROLE OF miRNA

• Over-expression of the maize Corngrass1 (Cg1) miRNA that belongs to the MIR156 family caused prolonged vegetative phase and delayed flowering resulting in increased biomass(Chuck et al., 2011) .

• It was reported that the degrees of morphological changes and biomass yields were related to the expression level of an exogenous rice miRNA Osa-miR156b (Fu et al., 2012).

• It was also observed that over-expression of rice miR156 could improve the yield of solubilized sugar as well as forage digestibility.

• miRNA can be silenced more quickly than other RNAs because has short nucleotide sequence or can be injected externally easily.

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