ABSTRACT
Small RNAs of 21-24 nucleotides (nt) have been found to play regulatory roles at the transcriptional and posttranscriptional levels in diverse eukaryotic organisms. Small RNAs are classified into microRNAs (miRNAs) and small interfering RNAs (siRNAs) based on their modes of biogenesis. miRNAs are derived from singlestranded precursor RNAs that form imperfect hairpin structures. siRNAs are produced from long double-stranded RNAs formed between two overlapping antisense RNAs or synthesized from single-stranded RNAs by the activities of RNA-dependent RNA polymerases. Plants appear to make extensive use of endogenous small RNAs to regulate gene expression in developmental processes and in response to abiotic and biotic stresses. Plants also use endogenous small RNAs to silence transposons to ensure genome stability.
