Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
DNA Res. 2019 Apr 1;26(2):171-182. doi: 10.1093/dnares/dsy047.
Dramatic changes occasionally occur in intergenic regions leading to genomic alterations during speciation and will consequently obscure the ancestral species that have contributed to the formation of allopolyploid organisms. The S genome of five species of section Sitopsis of genus Aegilops is considered to be an origin of B-genome in cultivated tetraploid and hexaploid wheat species, although its actual donor is still unclear. Here, we attempted to elucidate phylogenetic relationship among Sitopsis species by performing RNA sequencing of the coding regions of each chromosome. Thus, genome-wide polymorphisms were extensively analyzed in 19 accessions of the Sitopsis species in reference to the tetraploid and hexaploid wheat B genome sequences and consequently were efficiently anchored to the B-genome chromosomes. The results of our genome-wide exon sequencing and resultant phylogenetic analysis indicate that Ae. speltoides is likely to be the direct donor of all chromosomes of the wheat B genome. Our results also indicate that the genome differentiation during wheat allopolyploidization from S to B proceeds at different speeds over the chromosomes rather than at constant rate and recombination could be a factor determining the speed. This observation is potentially generalized to genome differentiation during plant allopolyploid evolution.
在物种形成过程中，基因间区域会发生剧烈变化，导致基因组发生改变，从而掩盖了形成异源多倍体生物的祖先物种。尽管其实际供体仍不清楚，但普通小麦栽培种的四倍体和六倍体中 B 基因组被认为来源于节节麦属 Sitopsis 组的 5 个种的 S 基因组。在这里，我们试图通过对每个染色体的编码区进行 RNA 测序来阐明 Sitopsis 种之间的系统发育关系。因此，我们参考四倍体和六倍体小麦 B 基因组序列，对 19 个 Sitopsis 种的材料进行了全基因组范围的多态性分析，并将其有效地锚定到 B 基因组染色体上。我们的全基因组外显子测序结果和系统发育分析表明，节节麦可能是小麦 B 基因组所有染色体的直接供体。我们的结果还表明，在小麦异源多倍体形成过程中，S 到 B 的基因组分化在染色体上的速度不同，而不是以恒定的速率进行，重组可能是决定速度的一个因素。这一观察结果可能推广到植物异源多倍体进化过程中的基因组分化。
