microRNA-directed phasing during trans-acting siRNA biogenesis in plants

Cell. 2005 Apr 22;121(2):207-21. doi: 10.1016/j.cell.2005.04.004.


Plants and animals use small RNAs (microRNAs [miRNAs] and siRNAs) as guides for posttranscriptional and epigenetic regulation. In plants, miRNAs and trans-acting (ta) siRNAs form through distinct biogenesis pathways, although they both interact with target transcripts and guide cleavage. An integrated approach to identify targets of Arabidopsis thaliana miRNAs and ta-siRNAs revealed several new classes of small RNA-regulated genes, including conventional genes such as Argonaute2 and an E2-ubiquitin conjugating enzyme. Surprisingly, five ta-siRNA-generating transcripts were identified as targets of miR173 or miR390. Rather than functioning as negative regulators, miR173- and miR390-guided cleavage was shown to set the 21-nucleotide phase for ta-siRNA precursor processing. These data support a model in which miRNA-guided formation of a 5' or 3' terminus within pre-ta-siRNA transcripts, followed by RDR6-dependent formation of dsRNA and Dicer-like processing, yields phased ta-siRNAs that negatively regulate other genes.

Publication types

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

MeSH terms

  • Arabidopsis / genetics*
  • Base Sequence
  • Gene Expression Profiling / methods
  • Gene Expression Profiling / standards
  • Gene Expression Regulation, Plant*
  • Genes, Plant / genetics
  • MicroRNAs / genetics*
  • Molecular Sequence Data
  • RNA, Small Interfering / genetics*
  • Reproducibility of Results
  • Transcription, Genetic / genetics


  • MicroRNAs
  • RNA, Small Interfering