Table_8_ATM Promotes RAD51-Mediated Meiotic DSB Repair by Inter-Sister-Chromatid Recombination in Arabidopsis.DOCX

Meiotic recombination ensures accurate homologous chromosome segregation during meiosis and generates novel allelic combinations among gametes. During meiosis, DNA double strand breaks (DSBs) are generated to facilitate recombination. To maintain genome integrity, meiotic DSBs must be repaired using appropriate DNA templates. Although the DNA damage response protein kinase Ataxia-telangiectasia mutated (ATM) has been shown to be involved in meiotic recombination in Arabidopsis, its mechanistic role is still unclear. In this study, we performed cytological analysis in Arabidopsis atm mutant, we show that there are fewer γH2AX foci, but more RAD51 and DMC1 foci on atm meiotic chromosomes. Furthermore, we observed an increase in meiotic Type I crossovers (COs) in atm. Our genetic analysis shows that the meiotic phenotype of atm rad51 double mutants is similar to the rad51 single mutant. Whereas, the atm dmc1 double mutant has a more severe chromosome fragmentation phenotype compared to both single mutants, suggesting that ATM functions in concert with RAD51, but in parallel to DMC1. Lastly, we show that atm asy1 double mutants also have more severe meiotic recombination defects. These data lead us to propose a model wherein ATM promotes RAD51-mediated meiotic DSB repair by inter-sister-chromatid (IS) recombination in Arabidopsis.

减数分裂重组（Meiotic recombination）可确保减数分裂过程中同源染色体的精准分离，并在配子中产生全新的等位基因组合。在减数分裂阶段，细胞会生成DNA双链断裂（DNA double strand breaks, DSBs）以启动重组过程。为维持基因组完整性，减数分裂产生的DSBs必须通过合适的DNA模板完成修复。尽管已有研究表明，DNA损伤响应蛋白激酶共济失调毛细血管扩张症突变激酶（Ataxia-telangiectasia mutated, ATM）参与拟南芥的减数分裂重组过程，但其具体作用机制仍未明确。本研究对拟南芥atm突变体开展了细胞学分析，结果显示，atm突变体的减数分裂染色体上的γH2AX焦点（γH2AX foci）数量减少，而RAD51与DMC1焦点的数量却显著增加。此外，我们还观察到atm突变体的I型减数分裂交换（Type I crossovers, COs）水平有所升高。遗传分析结果表明，atm rad51双突变体的减数分裂表型与rad51单突变体相似；而atm dmc1双突变体相较于两种单突变体，出现了更为严重的染色体碎片化表型，这提示ATM与RAD51协同发挥作用，但与DMC1的作用路径相互平行。最后，我们发现atm asy1双突变体同样存在更为严重的减数分裂重组缺陷。基于上述实验数据，我们提出了一个作用模型：在拟南芥中，ATM通过姐妹染色单体间重组（inter-sister-chromatid recombination, IS recombination）促进RAD51介导的减数分裂DSBs修复。