Genome sequence of the progenitor of the wheat D genome Aegilops tauschii

Corresponding author: Jan Dvořák

Aegilops tauschii (节节麦) is the diploid progenitor (二倍体祖先) of the D genome of hexaploid wheat (Triticum aestivum, genomes AABBDD) and an important genetic resource for wheat. The large size and highly repetitive nature of the Ae. tauschii genome has until now precluded (妨碍) the development of a reference-quality genome sequence. Here we use an array of advanced technologies, including ordered-clone (顺序克隆) genome sequencing , whole-genome shotgun sequencing, and BioNano optical genome mapping (光学图谱), to generate a reference-quality genome sequence for Ae. tauschii ssp. strangulata accession AL8/78, which is closely related to the wheat D genome. We show that compared to other sequenced plant genomes, including a much larger conifer genome, the Ae. tauschii genome contains unprecedented (前所未有的) amounts of very similar repeated sequences. Our genome comparisons reveal that the Ae. tauschii genome has a greater number of dispersed duplicated genes than other sequenced genomes and its chromosomes have been structurally evolving an order of magnitude (量级) faster than those of other grass genomes. The decay of colinearity with other grass genomes correlates with recombination rates along chromosomes. We propose that the vast amounts of very similar repeated sequences cause frequent errors in recombination and lead to gene duplications and structural chromosome changes that drive fast genome evolution.

节节麦是六倍体小麦（AABBDD）D套染色体的二倍体祖先，是小麦重要的遗传资源。节节麦的基因组较大且含大量重复序列，这些特征严重阻碍了参考基因组序列的获取。本文采用了顺序克隆基因组测序、全基因组鸟枪发测序和BioNano光学图谱等一系列新的测序技术获得了一个高质量的节节麦AL8/78参考级别的基因组序列。作者分析显示相比于其他包括针叶树种在内的已测序的植物基因组，节节麦的基因组存在前所未有的相似性重复序列。比较基因组分析显示节节麦的基因组相比于其他已测序的植物基因组含有更多的散生重复序列，且相比于其他草本基因组其染色体结构进化更快。节节麦基因组与其他草本植物基因组的共线性随着染色体上重组率而衰减。作者认为大量的相似性重复序列使得在重组中发生的错误频率增高，导致了基因重复和染色体结构性的改变，最终驱动了节节麦基因组的快速进化。

简单的来说，在大约6.5个百万年的时候小麦属（AA）与山羊草属（BB）分开，大约在5.5个百万年乌拉尔图小麦与山羊草杂交形成节节麦（DD），另外这两个种在大概小于0.8个百万年又杂交形成二粒小麦（AABB），最后在小于0.4个百万年节节麦与二粒小麦杂交形成了现在栽培的普通小麦（AABBDD），这也是普通小麦染色体是异源六倍体的原因。

节节麦从形态学上分为四类，分别是Ae. tauschii ssp.typica; ssp.anathera; ssp.meyeri; ssp.strangulata，其中ssp.typica; ssp.anathera和ssp.meyeri属于Ae. tauschii ssp.tauschii大类，Ae. tauschii ssp.strangulata单独为一类。（刘昆，2014，毕业论文：节节麦种子休眠评价及基因挖掘）

个人简介：1972年，萨斯喀彻温大学，博士。

doi: 10.1038/nature24486