背景回顾：MicroRNAs (miRNAs) are fast evolving endogenous small RNAs that regulate organism function and behaviour in both animals and plants. 

提出问题：Although models for de novo miRNA biogenesis have been proposed, the genomic mechanisms driving swift diversification of the miRNA repertoires in plants remain elusive. 

结果1-MITEs是miRNAs主要来源：Here, by comprehensively analysing 21 phylogenetically representative plant species, ranging from green algae to angiosperms, we systematically identified de novo miRNA events associated with 8,649 miRNA loci. We found that 399 (4.6%), 466 (5.4%), and 1,402 (16.2%) miRNAs were derived from inverted gene duplication events, long terminal repeats of retrotransposons, and miniature inverted-repeat transposable elements (MITEs), respectively. Among the miRNAs of these origins, MITEs, especially those belonging to the Mutator, Tc1/Mariner, and PIF/Harbinger superfamilies, were the predominant genomic source for de novo miRNAs in the 15 examined angiosperms but not in the six non-angiosperms. 

结果2-转座-转录：Our data further illustrated a transposition-transcription process by which MITEs are converted into new miRNAs (termed MITE-miRNAs) whereby properly sized MITEs are transcribed and therefore become potential substrates for the miRNA processing machinery by transposing into introns of active genes. 

结果2-植物适应性：By analysing the 58,038 putative target genes for the 8,095 miRNAs, we found that the target genes of MITE-miRNAs were preferentially associated with response to environmental stimuli such as temperature, suggesting that MITE-miRNAs are pertinent to plant adaptation.  

结论：Collectively, these findings demonstrate that molecular conversion of MITEs is a genomic mechanism leading to rapid and continuous changes to the miRNA repertoires in angiosperm.

Model for MITEs in shaping the miRNA repertoires in angiosperm.

miRNAs是演化最快的内源性小RNAs，调控动植物的生物体功能和行为。尽管miRNA从头生物发生的模型已经完备，但是植物中驱动miRNA快速多样化的基因组学基础并不清楚。本文中，作者分析了21个具有系统发育代表性的植物物种，从绿藻到被子植物，系统鉴定了这些植物中与8,649个miRNA位点相关的miRNA从头形成事件。作者发现分别有399、466、1402个miRNAs来自于反向基因重复事件、LRT逆转座子和MITE元件，分别占了4.6%、5.4%和16.2%。在这些miRNAs起源中，来自于Mutator、Tc1/Mariner和PIF/Harbinger超家族的MITEs明显在15个测试的被子植物基因组中从头miRNAs形成的来源，但是在其他6个非被子植物中则不然。作者的数据显示存在一个转座-转录的过程，在该过程中MITEs会被转化成新的miRNA（即MITE-miRNAs），由此正确大小的MITEs会被转录，从而通过转座到活跃基因的内含子中得以成为miRNA加工的潜在底物。通过分析8,095个miRNAs的58,038个假定候选基因，作者发现MITE-miRNAs的靶基因优先与温度等环境刺激响应基因相关，说明MITE-miRNAs与植物的适应性有关。综上，本文的发现揭示了MITEs的分子转化是被子植物miRNAs快速并持续改变的基因组学机制。

** 李 磊 **