title: A pathway for the biogenesis of trans-acting siRNAs in Arabidopsis.
abstract: The Arabidopsis genes, TAS2 and TAS1a, produce structurally similar noncoding transcripts that are transformed into short (21-nucleotide [nt]) and long (24-nt) siRNAs by RNA silencing pathways. Some of these short siRNAs direct the cleavage of protein-coding transcripts, and thus function as trans-acting siRNAs (ta-siRNAs). Using genetic analysis, we defined the pathway by which ta-siRNAs and other short siRNAs are generated from these loci. This process is initiated by the miR173-directed cleavage of a primary poly(A) transcript. The 3' fragment is then transformed into short siRNAs by the sequential activity of SGS3, RDR6, and DCL4: SGS3 stabilizes the fragment, RDR6 produces a complementary strand, and DCL4 cleaves the resulting double-stranded molecule into short siRNAs, starting at the end with the miR173 cleavage site and proceeding in 21-nt increments from this point. The 5' cleavage fragment is also processed by this pathway, but less efficiently. The DCL3-dependent pathway that generates long siRNAs does not require miRNA-directed cleavage and plays a minor role in the silencing of these loci. Our results define the core components of a post-transcriptional gene silencing pathway in Arabidopsis and reveal some of the features that direct transcripts to this pathway.
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6018, USA.
authors.forename: Manabu
authors.initials: M
authors.lastname: Yoshikawa
authors.forename: Angela
authors.initials: A
authors.lastname: Peragine
authors.forename: Mee Yeon
authors.initials: MY
authors.lastname: Park
authors.forename: R Scott
authors.initials: RS
authors.lastname: Poethig
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D018506:Gene Expression Regulation, Plant; D018390:Gene Targeting; D017343:Genes, Plant; D035683:MicroRNAs / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D012323:RNA Processing, Post-Transcriptional; D034741:RNA, Small Interfering / Q000096:biosynthesis*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D035683:MicroRNAs; D034741:RNA, Small Interfering