Fukui Prefectural University, Matsuoka, Eiheiji, Yoshida, Fukui, Japan.
PLoS One. 2013 Aug 8;8(8):e68310. doi: 10.1371/journal.pone.0068310. eCollection 2013.
The complex process of allopolyploid speciation includes various mechanisms ranging from species crosses and hybrid genome doubling to genome alterations and the establishment of new allopolyploids as persisting natural entities. Currently, little is known about the genetic mechanisms that underlie hybrid genome doubling, despite the fact that natural allopolyploid formation is highly dependent on this phenomenon. We examined the genetic basis for the spontaneous genome doubling of triploid F1 hybrids between the direct ancestors of allohexaploid common wheat (Triticum aestivum L., AABBDD genome), namely Triticumturgidum L. (AABB genome) and Aegilopstauschii Coss. (DD genome). An Ae. tauschii intraspecific lineage that is closely related to the D genome of common wheat was identified by population-based analysis. Two representative accessions, one that produces a high-genome-doubling-frequency hybrid when crossed with a T. turgidum cultivar and the other that produces a low-genome-doubling-frequency hybrid with the same cultivar, were chosen from that lineage for further analyses. A series of investigations including fertility analysis, immunostaining, and quantitative trait locus (QTL) analysis showed that (1) production of functional unreduced gametes through nonreductional meiosis is an early step key to successful hybrid genome doubling, (2) first division restitution is one of the cytological mechanisms that cause meiotic nonreduction during the production of functional male unreduced gametes, and (3) six QTLs in the Ae. tauschii genome, most of which likely regulate nonreductional meiosis and its subsequent gamete production processes, are involved in hybrid genome doubling. Interlineage comparisons of Ae. tauschii's ability to cause hybrid genome doubling suggested an evolutionary model for the natural variation pattern of the trait in which non-deleterious mutations in six QTLs may have important roles. The findings of this study demonstrated that the genetic mechanisms for hybrid genome doubling could be studied based on the intrinsic natural variation that exists in the parental species.
异源多倍体形成的复杂过程包括各种机制，从种间杂交和杂种基因组加倍到基因组改变以及新异源多倍体作为持续存在的自然实体的确立。尽管自然异源多倍体的形成高度依赖于这种现象，但目前对于导致杂种基因组加倍的遗传机制知之甚少。我们研究了异源六倍体普通小麦（AABBDD 基因组）的直接祖先——节节麦（AABB 基因组）和粗山羊草（DD 基因组）之间的三倍体 F1 杂种自发基因组加倍的遗传基础。通过基于群体的分析，鉴定出一个与普通小麦 D 基因组密切相关的粗山羊草种内谱系。从该谱系中选择了两个代表性品系，一个与节节麦品种杂交时产生高基因组加倍频率的杂种，另一个与同一品种杂交时产生低基因组加倍频率的杂种，用于进一步分析。一系列研究包括育性分析、免疫染色和数量性状位点（QTL）分析表明：（1）通过非减数分裂产生有功能的未减数配子是成功杂种基因组加倍的早期关键步骤；（2）第一次分裂后恢复是导致有功能的雄性未减数配子减数分裂中非减数的细胞学机制之一；（3）粗山羊草基因组中的 6 个 QTL 参与了杂种基因组加倍，其中大多数可能调节非减数减数分裂及其随后的配子产生过程。粗山羊草引起杂种基因组加倍能力的种间比较表明，该性状的自然变异模式存在进化模型，其中六个 QTL 中的非有害突变可能具有重要作用。本研究的结果表明，可以基于亲本物种中存在的内在自然变异来研究杂种基因组加倍的遗传机制。
