Plant small RNAs: advancement in the understanding of biogenesis and role in plant development.

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CONCLUSION: Present review addresses the advances made in the understanding of biogenesis of plant small RNAs and their role in plant development. We discuss the elaborate role of microRNAs (miRNAs) and trans-acting small interfering RNAs (ta-siRNAs) in various aspects of plant growth and development and highlight relevance of small RNA mobility. Small non-coding RNAs regulate various aspects of plant development. Small RNAs (sRNAs) of 21-24 nucleotide length are derived from double-stranded RNAs through the combined activity of several biogenesis and processing components. These sRNAs function by negatively regulating the expression of target genes. miRNAs and ta-siRNAs constitute two important classes of endogenous small RNAs in plants, which play important roles in plant growth and developmental processes like embryogenesis, organ formation and patterning, shoot and root growth, and reproductive development. Biogenesis of miRNAs is a multistep process which includes transcription, processing and modification, and their loading onto RNA-induced silencing complex (RISC). RISC-loaded miRNAs carry out post-transcriptional silencing of their target(s). Recent studies identified orthologues of different biogenesis components of novel and conserved small RNAs from different model plants. Although many small RNAs have been identified from diverse plant species, only a handful of them have been functionally characterized. In this review, we discuss the advances made in understanding the biogenesis, functional conservation/divergence in miRNA-mediated gene regulation, and the developmental role of small RNAs in different plant species.