Abstract
Since transposons are potentially highly mutagenic, the majority of them are epigenetically silenced by RNA silencing machinary. However, most proportion of the eukaryotic genome is composed of transposoable elements. This indicates that transposons have likely evolved countermeasures to transposon silencing.
Here we show that a class of transposons in rice utilizes a microRNA (miRNA) as a strategy to suppress silencing. We found that miR820 family is a miRNAs, which are expressed from CACTA DNA transposons in rice and whose target is a DNA methyltransferase gene, OsDRM1a, one of the components of epigenetic silencing. First, we tested if miR820 regulates the expression of OsDRM1a by using small RNA deficient mutant in rice. In this mutant, the expression level of miR820 and OsDRM1a reduced and increased, respectively. This result indicates that miR820 negatively regulates the expression of OsDRM1a. Next, we suppressed the expression of OsDRM1a by RNA interference. This resulted in increase of transposon encoded gene expression. Taken together, our results demonstrate that miR820 suppresses transposon silencing by down-regulation of OsDRM1a expression.
