MicroRNA-mediated DNA methylation in plants

DNA methylation, a major event in epigenetics, plays an essential role in the control of gene expression. Increasing evidence suggests that long and short non-coding RNAs are involved extensively in plants to direct the establishment, spread, and removal of DNA cytosine methylation throughout their genomes. Yet, little has been known about the role of microRNAs (miRNAs) in DNA methylation although the role of small interfering RNAs (siRNAs) in DNA methylation has been well established. Several recent studies, however, provided the evidence for miRNA-directed DNA methylation in plants, and the working mechanisms still need to be fully explored. In this review, we highlight the key features of miRNA-directed DNA methylation in plants and provide insight into the complexities of such an event in plants. The interaction between miRNAs and the epigenetic machinery and the future potential research questions are briefly discussed.