Meiotic recombination is initiated by formation of DNA double‐strand breaks (DSBs). This involves a protein complex that includes in plants the two similar proteins, SPO11‐1 and SPO11‐2. We analysed the sequences of SPO11‐2 in hexaploid bread wheat (Triticum aestivum), as well as in its diploid and tetraploid progenitors. We investigated its role during meiosis using single, double and triple mutants. The three homoeologous SPO11‐2 copies of hexaploid wheat exhibit high nucleotide and amino acid similarities with those of the diploids, tetraploids and Arabidopsis. Interestingly, however, two nucleotides deleted in exon‐2 of the A copy lead to a premature stop codon and suggest that it encodes a non‐functional protein. Remarkably, the mutation was absent from the diploid A‐relative Triticum urartu, but present in the tetraploid Triticum dicoccoides and in different wheat cultivars indicating that the mutation occurred after the first polyploidy event and has since been conserved. We further show that triple mutants with all three copies (A, B, D) inactivated are sterile. Cytological analyses of these mutants show synapsis defects, accompanied by severe reductions in bivalent formation and numbers of DMC1 foci, thus confirming the essential role of TaSPO11‐2 in meiotic recombination in wheat. In accordance with its 2‐nucleotide deletion in exon‐2, double mutants for which only the A copy remained are also sterile. Notwithstanding, some DMC1 foci remain visible in this mutant, suggesting a residual activity of the A copy, albeit not sufficient to restore fertility.

中文翻译：

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SPO11.2对于面包小麦（Triticum aestivum L.）减数分裂过程中程序化的双链断裂形成至关重要。

减数分裂重组是通过DNA双链断裂（DSB）的形成而开始的。这涉及一种蛋白质复合物，在植物中包括两种相似的蛋白质SPO11-1和SPO11-2。我们分析了六倍体面包小麦（Triticum aestivum）及其二倍体和四倍体祖细胞中SPO11-2的序列。我们使用单，双和三突变体调查了它在减数分裂过程中的作用。六倍体小麦的三个同源SPO11-2副本与二倍体，四倍体和拟南芥具有高度的核苷酸和氨基酸相似性。然而，有趣的是，A拷贝第2外显子缺失的两个核苷酸会导致过早的终止密码子，提示它编码的是非功能蛋白。值得注意的是，二倍体A相对小麦，但存在于四倍体麦冬中和不同的小麦品种中，表明该突变在第一次多倍体事件后发生，并且此后一直被保存。我们进一步表明灭活了所有三个副本（A，B，D）的三重突变体是无菌的。这些突变体的细胞学分析显示突触缺陷，伴随着二价形成和DMC1病灶数量的严重减少，从而证实了TaSPO11-2在小麦减数分裂重组中的重要作用。根据外显子2中2核苷酸的缺失，仅保留A拷贝的双突变体也是不育的。尽管如此，一些DMC1病灶仍在此突变体中可见，表明A拷贝的残留活性，尽管不足以恢复生育力。