Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA.
Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA.
Nat Genet. 2018 Feb;50(2):186-192. doi: 10.1038/s41588-017-0032-5. Epub 2018 Jan 15.
Chromosome dosage has substantial effects on reproductive isolation and speciation in both plants and animals, but the underlying mechanisms are largely obscure . Transposable elements in animals can regulate hybridity through maternal small RNA , whereas small RNAs in plants have been postulated to regulate dosage response via neighboring imprinted genes. Here we show that a highly conserved microRNA in plants, miR845, targets the tRNA primer-binding site (PBS) of long terminal repeat (LTR) retrotransposons in Arabidopsis pollen, and triggers the accumulation of 21-22-nucleotide (nt) small RNAs in a dose-dependent fashion via RNA polymerase IV. We show that these epigenetically activated small interfering RNAs (easiRNAs) mediate hybridization barriers between diploid seed parents and tetraploid pollen parents (the 'triploid block'), and that natural variation for miR845 may account for 'endosperm balance' allowing the formation of triploid seeds. Targeting of the PBS with small RNA is a common mechanism for transposon control in mammals and plants, and provides a uniquely sensitive means to monitor chromosome dosage and imprinting in the developing seed.
染色体剂量对动植物的生殖隔离和物种形成有很大的影响，但潜在的机制在很大程度上还不清楚。动物中的转座元件可以通过母系小分子 RNA 来调节杂种的形成，而植物中的小分子 RNA 被认为可以通过相邻的印迹基因来调节剂量反应。在这里，我们表明，在拟南芥花粉中，一种高度保守的植物 microRNA（miR845）靶向长末端重复（LTR）逆转座子的 tRNA 引物结合位点（PBS），并通过 RNA 聚合酶 IV 以剂量依赖的方式触发 21-22 核苷酸（nt）小分子 RNA 的积累。我们表明，这些表观遗传激活的小干扰 RNA（easiRNA）介导了二倍体种子亲本和四倍体花粉亲本之间的杂交障碍（“三倍体阻断”），并且 miR845 的自然变异可能解释了“胚乳平衡”，允许三倍体种子的形成。小分子 RNA 对 PBS 的靶向是哺乳动物和植物中转座子控制的一种常见机制，为监测发育中的种子中的染色体剂量和印迹提供了一种独特的敏感手段。
