• Many flowering plant taxa contain allopolyploids that share one or more genomes in common. In the Brassica genus, crop species Brassica juncea and Brassica carinata share the B genome, with 2n = AABB and 2n = BBCC genome complements, respectively. Hybridization results in 2n = BBAC hybrids, but the fate of these hybrids over generations of self‐pollination has never been reported.
• We produced and characterized B. juncea × B. carinata (2n = BBAC) interspecific hybrids over six generations of self‐pollination under selection for high fertility using a combination of genotyping, fertility phenotyping, and cytogenetics techniques.
• Meiotic pairing behaviour improved from 68% bivalents in the F₁ to 98% in the S₅/S₆ generations, and initially low hybrid fertility also increased to parent species levels. The S₅/S₆ hybrids contained an intact B genome (16 chromosomes) plus a new, stable A/C genome (18–20 chromosomes) resulting from recombination and restructuring of A and C‐genome chromosomes.
• Our results provide the first experimental evidence that two genomes can come together to form a new, restructured genome in hybridization events between two allotetraploid species that share a common genome. This mechanism should be considered in interpreting phylogenies in taxa with multiple allopolyploid species.

中文翻译：

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通过异源四倍体芥菜油菜（AABB）和芸苔油菜（BBCC）杂交产生的稳定，可育的系已融合了A和C基因组

• 许多开花植物类群包含同种多倍体，它们共有一个或多个基因组。在芸苔属中，农作物芸苔属和芸苔属共享B基因组，分别具有2 n  = AABB和2 n  = BBCC基因组互补序列。杂交产生2 n  = BBAC杂种，但这些杂种在自花授粉世代中的命运尚未见报道。
• 我们 通过基因分型，育性表型和细胞遗传学技术的结合，在经过六代自花授粉的高生育力选择下，产生并鉴定了芥菜型×芥子型（2 n = BBAC）种间杂种。
• 减数分裂配对行为从F ₁中的68％二价提高到S ₅ / S ₆世代中的98％，并且最初的低杂种育性也增加到了亲本水平。S ₅ / S ₆杂种包含一个完整的B基因组（16个染色体）和一个新的，稳定的A / C基因组（18-20个染色体），这是由A和C基因组染色体的重组和重组产生的。
• 我们的结果提供了第一个实验证据，即在共享同一基因组的两个同种四倍体物种之间的杂交事件中，两个基因组可以聚在一起形成一个新的，重组的基因组。在解释具有多种同种多倍体物种的类群中的系统发育时，应考虑该机制。