Published in
Nature Research, Nature Structural and Molecular Biology, 8(17), p. 997-1003, 2010
DOI: 10.1038/nsmb.1866
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- [www.ncbi.nlm.nih.gov] | PDF
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Unique Functionality of 22 nt miRNAs in Triggering RDR6-Dependent siRNA Biogenesis from Target Transcripts in Arabidopsis
,
Alberto Carbonell ,
Noah Fahlgren,
Hernan Garcia-Ruiz,
Russell T. Burke,
Atsushi Takeda,
Christopher M. Sullivan,
Sunny D. Gilbert,
Taiowa A. Montgomery ,
James C. Carrington
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Abstract
RNA interference pathways can involve amplification of secondary siRNAs by RNA-dependent RNA polymerases. In plants, RDR6-dependent secondary siRNAs arise from transcripts targeted by some microRNAs (miRNAs). Here, Arabidopsis thaliana secondary siRNAs from mRNA as well as trans-acting siRNAs are shown to be triggered through initial targeting by a 22-nucleotide (nt) miRNA that associates with AGO1. In contrast to canonical 21-nt miRNAs, 22-nt miRNAs primarily arise from foldback precursors containing asymmetric bulges. Using artificial miRNA constructs, conversion of asymmetric foldbacks to symmetric foldbacks resulted in the production of 21-nt forms of miR173, miR472 and miR828. Both 21- and 22-nt forms associated with AGO1 and guided accurate slicer activity, but only 22-nt forms were competent to trigger RDR6-dependent siRNA production from target RNA. These data suggest that AGO1 functions differentially with 21- and 22-nt miRNAs to engage the RDR6-associated amplification apparatus.