Post-transcriptional Regulation of MicroRNA Accumulation and Function: New Insights from Plants  Zofia Szweykowska-Kulinska, Artur Jarmolowski  Molecular Plant  Volume 11, Issue 8, Pages 1006-1007 (August 2018) DOI: 10.1016/j.molp.2018.06.010 Copyright © 2018 The Author Terms and Conditions

Figure 1 Post-transcriptional Events that Control the Level and Function of Plant miRNAs. The miRNA level can be controlled by splicing. (1) Alternative splicing of the pre-mRNA hosting a miRNA in its intron causes the accumulation of the splice isoform, which cannot be processed efficiently by the miRNA biogenesis machinery (Yan et al., 2012). (2) Selected miRNAs encoded within exons (exonic miRNAs) of pri-miRNAs are upregulated in the case of efficient splicing, while the miRNAs that are encoded within introns (intronic miRNAs) are upregulated when splicing is impaired. Active 5′ splice sites stimulate biogenesis of exonic miRNAs but downregulate the production of intronic miRNAs (Schwab et al., 2013; Knop et al., 2017). In the case of some miRNAs that are encoded within introns of protein-coding genes, impaired splicing of their host pre-mRNAs can activate alternative polyadenylation sites producing short, intronless transcripts from which miRNAs are efficiently processed (Knop et al., 2017). The CHR2 RNA helicase is involved in remodeling of pri-miRNAs that are bound by SERRATE. This CHR2 activity inhibits miRNA processing (Wang et al., 2018). Pri-miRNAs can be folded in such way that alternative stem and loop structures can be formed that allows alternate maturation, sorting, and activities of miRNAs (Iki et al., 2018). The 2′O methylation of miRNA/miRNA* duplexes at their 3′ ends stabilizes both molecules and protects them from oligouridylation and degradation (Park et al., 2002). AGO1 stabilizes the levels of selected miRNAs in the cytoplasm during stress (Dolata et al., 2016). Exoribonucleases of the SDN (SMALL RNA DEGRADING) family degrade mature miRNAs and therefore can influence the final levels of miRNAs (Ramachandran and Chen, 2008). Molecular Plant 2018 11, 1006-1007DOI: (10.1016/j.molp.2018.06.010) Copyright © 2018 The Author Terms and Conditions