Chromosome dosage has substantial effects on reproductive isolation and speciation in both plants and animals, but the underlying mechanisms are largely obscure ¹ . Transposable elements in animals can regulate hybridity through maternal small RNA ² , whereas small RNAs in plants have been postulated to regulate dosage response via neighboring imprinted genes^3,4. Here we show that a highly conserved microRNA in plants, miR845, targets the tRNA^Met 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.

中文翻译：

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由 miR845 触发的转座子衍生的小 RNA 介导拟南芥基因组剂量反应。


染色体剂量对植物和动物的生殖隔离和物种形成具有重大影响，但其潜在机制在很大程度上尚不清楚¹ 。动物中的转座元件可以通过母体小 RNA 调节杂交² ，而植物中的小 RNA 被认为可以通过邻近的印记基因调节剂量反应^3,4 。在这里，我们发现植物中高度保守的 microRNA miR845 靶向拟南芥花粉中长末端重复 (LTR) 反转录转座子的 tRNA ^Met引物结合位点 (PBS)，并触发 21-22 核苷酸 (nt) 小片段的积累RNA 通过 RNA 聚合酶 IV 以剂量依赖性方式产生。我们发现，这些表观遗传激活的小干扰 RNA (easiRNA) 介导二倍体种子亲本和四倍体花粉亲本（“三倍体块”）之间的杂交障碍，并且 miR845 的自然变异可能解释“胚乳平衡”，从而允许三倍体种子的形成。用小 RNA 靶向 PBS 是哺乳动物和植物中转座子控制的常见机制，并提供了一种独特的灵敏方法来监测发育种子中的染色体剂量和印记。