MicroRNAs transcriptionally regulate promoter activity in Arabidopsis thaliana: miRNAs activate target promoters in Arabidopsis

MicroRNAs (miRNAs) are vital regulators that repress gene expression in the cytoplasm in two main ways: mRNA degradation and translational inhibition. Several animal studies have shown that miRNAs also target promoters, thereby activating expression. Whether this miRNA action also occurs in plants is unknown. In this study, we demonstrated that several miRNAs regulate target promoters in Arabidopsis thaliana. For example, miR5658 was predominantly present in the nucleus and activated the expression of AT3G25290 directly by binding to its promoter. Our observations suggest that this mode of action may be a general feature of plant miRNAs, and thus provide insight into the vital roles of plant miRNAs in the nucleus.