Addo Nyarko Charles, Katche Elvis, Báez Mariana, Lv Zhenling, Mason Annaliese S
Plant Breeding Department, INRES, University of Bonn, Kirschallee 1, 53115, Bonn, Germany.
Plant Breeding Department, Justus Liebig University, Heinrich-Buff-Ring 26-32, 35392, Giessen, Germany.
Heredity (Edinb). 2025 Feb;134(2):98-108. doi: 10.1038/s41437-024-00738-6. Epub 2024 Nov 30.
The establishment of successful interspecies hybrids requires restoration of a stable "2n" chromosome complement which can produce viable "n" gametes. This may occur (rarely) via recombination between non-homologous chromosomes, or more commonly is associated with a doubling of parental chromosome number to produce new homologous pairing partners in the hybrid. The production of unreduced "2n" gametes (gametes with the somatic chromosome number) may therefore be evolutionarily useful by serving as a key pathway for the formation of new polyploid hybrids, as might specific mechanisms permitting recombination between non-homologous chromosomes. Here, we investigated chromosome complements and fertility in third generation interspecific hybrids (AABC) resulting from a cross between allopolyploids Brassica juncea (AABB) × B. napus (AACC) followed by self-pollination for two generations. Chromosome numbers ranged from 2n = 48-74 in the experimental population (35 plants), with 9-16 B genome chromosomes and up to 4 copies of A genome chromosomes. Unreduced gamete production leading to a putative genome structure of approximately AAAABBCC was hence predicted to explain the high chromosome numbers observed. Additionally, the estimation of nuclei number in post-meiotic sporads revealed a higher frequency of unreduced gametes (0.04-5.21%) in the third generation AABC interspecific hybrids compared to the parental Brassica juncea (0.07%) and B. napus (0.13%). Our results suggest that unreduced gamete production in the subsequent generations following interspecific hybridization events may play a critical role in restoration of more stable, fertile chromosome complements.
成功建立种间杂种需要恢复稳定的“2n”染色体组，该染色体组能够产生可育的“n”配子。这可能（很少）通过非同源染色体之间的重组发生，或者更常见的是与亲本染色体数目的加倍相关，从而在杂种中产生新的同源配对伙伴。因此，未减数的“2n”配子（具有体细胞染色体数目的配子）的产生可能在进化上是有用的，因为它是形成新的多倍体杂种的关键途径，允许非同源染色体之间重组的特定机制也可能如此。在这里，我们研究了异源多倍体芥菜（AABB）×甘蓝型油菜（AACC）杂交后自花授粉两代产生的第三代种间杂种（AABC）的染色体组和育性。实验群体（35株植物）的染色体数范围为2n = 48 - 74，有9 - 16条B基因组染色体和多达4份A基因组染色体拷贝。因此，预计未减数配子的产生导致假定的基因组结构约为AAAABBCC，以解释观察到的高染色体数。此外，减数分裂后孢子体中细胞核数目的估计显示，与亲本芥菜（0.07%）和甘蓝型油菜（0.13%）相比，第三代AABC种间杂种中未减数配子的频率更高（0.04 - 5.21%）。我们的结果表明，种间杂交事件后后代中未减数配子的产生可能在恢复更稳定、可育的染色体组方面发挥关键作用。
