ABSTRACT
Plant small RNAs, which range in size from approximately 20-30 nucleotides (nt), can be distinguished both by their biogenesis and mode of action. They include microRNAs (miRNAs) and small interfering RNAs (siRNAs) such as repeat-associated siRNAs (ra-siRNAs), trans-acting siRNAs (ta-siRNAs), and natural antisense transcript siRNAs (nat-siRNAs) (Vaucheret 2006). Each type of small RNA is unique with respect to length, the plant DICER-like (DCL) endonucleases that are involved in its biogenesis pathway, and the ARGONAUTE (AGO) proteins that are small RNA guides for target silencing. Most siRNAs target the same locus they were derived from, except for miRNAs and ta-siRNAs, which target mRNAs from different loci. All small RNA molecules may function as negative regulators of gene expression (Ruiz-Ferrer and Voinnet 2009).
