背景回顾：Common wheat (Triticum aestivum L., BBAADD) is a major staple food crop worldwide. The diploid progenitors of the A- and D-subgenomes have been unequivocally identified, that of B however remains ambiguous and controversial but is suspected to be related to species of Aegilops,section Sitopsis. 

主要研究：Here, we report the assembly of chromosome-level genome sequences of all five Sitopsis species, namely Ae. bicornis, Ae. longissima, Ae. searsii, Ae. sharonensis, and Ae. speltoides, as well as partial assembly of Amblyopyrum muticum (synonymous Aegilops mutica) genome for phylogenetic analysis. 

结果1-B亚基因组供体：Our results support that the donor of common wheat B-subgenome is a distinct, and most probably extinct, diploid species that diverged from an ancestral progenitor of the B-lineage to which the still extant Ae. speltoides and Am. muticum belong. 

结果2-种间遗传渐渗：In addition, we identified inter-specific genetic introgressions throughout the evolution of the Triticum/Aegilops species complex. 

结果3-共线性：The five Sitopsis species have variable assembled genome sizes (4.11-5.89 Gb) with high proportions of repetitive sequences (85.99-89.81%); nonetheless, they retain high collinearitywith other genomes or subgenomes of species in the Triticum/Aegilops complex. 

结果4-基因组大小变异：Differences in genome sizewere primarily due to independent post-speciation amplification of transposons. 

结果5-农艺性状相关基因：We also identified a set of Sitopsis genes pertinent to important agronomic traits that can be harnessed for wheat breeding. 

结论：These newly assembled genome resources provide a new roadmap for evolutionary and genetic studies of the Triticum/Aegilops complex, as well as for wheat improvement.

 摘 要 

六倍体普通小麦（Triticum aestivum, BBAADD）是全球范围内的主要粮食作物。其中，A和D套亚基因组的二倍体祖先已经十分明确，但是B套亚基因组的二倍体祖先还存在争议，目前比较明确的就是其肯定来自于山羊草属Sitopsis组的物种。本文中，作者组装了所有Sitopsis组的5个物种的染色体水平基因组，即二角山羊草（Aegilops bicornis）、高大山羊草（Aegilops longissima）、西尔斯山羊草（Aegilops searsii）、沙融山羊草（Aegilops sharonensis）和拟斯卑尔脱山羊草（Aegilops speltoides）；另外，作者还部分组装了无芒山羊草（Aegilops mutica）的基因组用于系统发育分析。研究结果表明，六倍体普通小麦中的B套亚基因组的供体是一个可能已经灭绝的、不同于所有现存山羊草属Sitopsis组的二倍体物种，其分化自现存拟斯卑尔脱山羊草和无芒山羊草所属的B-lineage的祖先物种。另外，作者还鉴定了小麦-山羊草复合群在演化过程中的种间特异性遗传渐渗。五个Sitopsis组物种的基因组在大小上存在差异，从4.11Gb到5.89Gb不等，并且具有高水平的重复序列（85.99-89.81%）；然而，它们与小麦-山羊草复合群其它物种的基因组或亚基因组之间存在高度的共线性关系。基因组大小的差异主要是由于独立的物种分化后转座子扩张所导致的。作者还鉴定了一系列与重要农艺性状相关的Sitopsis基因，可用于未来小麦的育种改良。这些新组装的基因组资源为小麦-山羊草复合群的演化和遗传研究，以及小麦的育种改良提供了新的思路。