Unique functionality of 22-nt miRNAs in triggering RDR6-dependent siRNA biogenesis from target transcripts in Arabidopsis

Nat Struct Mol Biol. 2010 Aug;17(8):997-1003. doi: 10.1038/nsmb.1866. Epub 2010 Jun 18.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / genetics*
  • Arabidopsis Proteins / metabolism*
  • Base Sequence
  • Gene Expression Regulation, Plant
  • MicroRNAs / chemistry
  • MicroRNAs / genetics
  • MicroRNAs / metabolism*
  • Molecular Sequence Data
  • Nucleic Acid Conformation
  • Nucleotides / genetics*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Small Interfering / biosynthesis*
  • RNA, Small Interfering / chemistry
  • RNA, Small Interfering / genetics
  • RNA-Dependent RNA Polymerase / metabolism*


  • Arabidopsis Proteins
  • MicroRNAs
  • Nucleotides
  • RNA, Messenger
  • RNA, Small Interfering
  • RDR6 protein, Arabidopsis
  • RNA-Dependent RNA Polymerase

Associated data

  • GEO/GSE22252