title: A diverse and evolutionarily fluid set of microRNAs in Arabidopsis thaliana.
abstract: To better understand the diversity of small silencing RNAs expressed in plants, we employed high-throughput pyrosequencing to obtain 887,000 reads corresponding to Arabidopsis thaliana small RNAs. They represented 340,000 unique sequences, a substantially greater diversity than previously obtained in any species. Most of the small RNAs had the properties of heterochromatic small interfering RNAs (siRNAs) associated with DNA silencing in that they were preferentially 24 nucleotides long and mapped to intergenic regions. Their density was greatest in the proximal and distal pericentromeric regions, with only a slightly preferential propensity to match repetitive elements. Also present were 38 newly identified microRNAs (miRNAs) and dozens of other plausible candidates. One miRNA mapped within an intron of DICER-LIKE 1 (DCL1), suggesting a second homeostatic autoregulatory mechanism for DCL1 expression; another defined the phase for siRNAs deriving from a newly identified trans-acting siRNA gene (TAS4); and two depended on DCL4 rather than DCL1 for their accumulation, indicating a second pathway for miRNA biogenesis in plants. More generally, our results revealed the existence of a layer of miRNA-based control beyond that found previously that is evolutionarily much more fluid, employing many newly emergent and diverse miRNAs, each expressed in specialized tissues or at low levels under standard growth conditions.
authors.affiliation: Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA.
authors.forename: Ramya
authors.initials: R
authors.lastname: Rajagopalan
authors.forename: Hervé
authors.initials: H
authors.lastname: Vaucheret
authors.forename: Jerry
authors.initials: J
authors.lastname: Trejo
authors.forename: David P
authors.initials: DP
authors.lastname: Bartel
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000378:metabolism; D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000378:metabolism; D018076:DNA, Complementary; D018506:Gene Expression Regulation, Plant; D015723:Gene Library; D035683:MicroRNAs / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D018749:RNA, Plant / Q000737:chemistry / Q000235:genetics; D034741:RNA, Small Interfering / Q000737:chemistry / Q000235:genetics; D043244:Ribonuclease III / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism; D017423:Sequence Analysis, RNA
chemical_list: D029681:Arabidopsis Proteins; D018797:Cell Cycle Proteins; D018076:DNA, Complementary; D035683:MicroRNAs; D018749:RNA, Plant; D034741:RNA, Small Interfering; C504982:DCL4 protein, Arabidopsis; D012260:Ribonucleases; C402383:DCL1 protein, Arabidopsis; D043244:Ribonuclease III