Plant Biotechnology, Faculty of Biology, University of Freiburg, Schaenzlestrasse 1, 79104 Freiburg, Germany.
Cell. 2010 Jan 8;140(1):111-22. doi: 10.1016/j.cell.2009.12.023.
MicroRNAs (miRNAs) control gene expression in animals and plants. Like another class of small RNAs, siRNAs, they affect gene expression posttranscriptionally. While siRNAs in addition act in transcriptional gene silencing, a role of miRNAs in transcriptional regulation has been less clear. We show here that in moss Physcomitrella patens mutants without a DICER-LIKE1b gene, maturation of miRNAs is normal but cleavage of target RNAs is abolished and levels of these transcripts are drastically reduced. These mutants accumulate miRNA:target-RNA duplexes and show hypermethylation of the genes encoding target RNAs, leading to gene silencing. This pathway occurs also in the wild-type upon hormone treatment. We propose that initiation of epigenetic silencing by DNA methylation depends on the ratio of the miRNA and its target RNA.
微小 RNA（miRNA）在动植物中控制基因表达。与另一类小 RNA，即 siRNA 一样，它们在后转录水平影响基因表达。虽然 siRNA 还可以在转录基因沉默中发挥作用，但 miRNA 在转录调控中的作用还不太清楚。我们在这里表明，在没有 DICER-LIKE1b 基因的苔藓植物Physcomitrella patens 突变体中，miRNA 的成熟是正常的，但靶 RNA 的切割被废除，并且这些转录物的水平大大降低。这些突变体积累 miRNA:target-RNA 双链体，并显示靶 RNA 编码基因的超甲基化，导致基因沉默。在激素处理下，这种途径也会在野生型中发生。我们提出，DNA 甲基化引发的表观遗传沉默的启动取决于 miRNA 和其靶 RNA 的比例。
