LAUSR

For many years we have studied the processes involved in producing microRNAs (miRNAs) in plants and the numerous differences with the metazoan counterpart. A well-defined catalytic process, mostly carried out by the RNase III enzyme DICER-LIKE1 (DCL1), was early identified after discovering RNAi and followed by the isolation of a plethora of miRNA biogenesis co-factors. The production of miRNAs, which later are loaded in ARGONAUTE (AGO) proteins to perform their RNA silencing functions both within the cell and non-cell autonomously, appears to be a highly regulated and dynamic process. Many regulatory events during miRNA biogenesis require the action of specific proteins. However, in recent years, many post-transcriptional modifications, structural features, and coupling with other cellular processing emerged as critical elements controlling the production of miRNA and, thus, plants' physiology. This review discusses new evidence that has changed the way we understand how miRNAs are produced in plants. We also provide an updated view of the miRNA biogenesis pathways, focusing on the gaps in our knowledge and the most compelling questions that remain open.