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Small-RNAs are 20 to 27 nucleotides long non-protein-coding RNAs that act on either DNA or RNA to effect the regulation of gene expression. Small-RNAs are key in genetic and epigenetic regulation of diverse biological processes and pathways in response to biotic and abiotic environmental stresses. The gene regulatory functions of small-RNA molecules enhance healthy plant growth and normal development by controlling biological processes such as flowering programming, fruit development, disease and pests resistance. Small-RNAs comprise mainly microRNA and small interfering RNA species. MicroRNAs have been proven to primarily engage in posttranscriptional gene regulation while small interfering RNA have been implicated mainly in transcriptional gene regulation. This review covers the recent advancements in small-RNA research in plants, with emphasis on particularly microRNAs and small interfering RNA biogenesis, biological functions and their relevance in the regulation of traits of agronomic importance in plants. Also discussed extensively is the potential biotechnological applications of these small-RNAs for crop improvement.
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