Nucleic Acids Research Advance Access published online on February 2, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp031
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Adenylation of plant miRNAs
Forest Biotechnology Group, Department of Forestry and Environmental Resources, College of Natural Resources, North Carolina State University, Raleigh, NC 27695, USA
*To whom correspondence should be addressed. Tel: +1 919 513 0074; Fax: +1 919 515 7801; Email: slu{at}unity.ncsu.edu
Received June 30, 2008. Revised January 6, 2009. Accepted January 8, 2009.
The modification or degradation of RNAs including miRNAs may play vital roles in regulating RNA functions. The polyadenylation- and exosome-mediated RNA decay is involved in the degradation of plant RNAs including the primary miRNA processing intermediates. However, plant miRNA levels are not affected by exosome depletion. Here, we report the cloning of a large number of 5' and/or 3' truncated versions of the known miRNAs from various tissues of Populus trichocarpa (black cottonwood). It suggests that plant miRNAs may be degraded through either 5' to 3' or 3' to 5' exonucleolytic digestion. We also show that a significant portion of the isolated miRNAs contains, at the 3'-end, one or a few post-transcriptionally added adenylic acid residues, which are distinct in length from the polyadenylate tail added to other plant RNAs for exosome-mediated degradation. Using an in vitro miRNA degradation system, where synthesized miRNA oligos were degraded in extracts of P. trichocarpa cells, we revealed that the adenylated miRNAs were degraded slower than others without adenylation. It indicates that addition of adenylic acid residues on the 3'-end plays a negative role in miRNA degradation. Our results provide new information for understanding the mechanism of miRNA degradation.