Endogenous small (sm) RNAs (primarily si- and miRNAs) are important trans/cis-acting regulators involved in diverse cellular functions. In plants, the RNA-dependent RNA polymerases (RDRs) are essential for smRNA biogenesis. | Mutation of the RDR1 gene caused genome-wide changes in gene expression regional variation in small RNA clusters and localized alteration in DNA methylation in rice