Key Laboratory of Plant Functional Genomics of Ministry of Education/Jiangsu Key Laboratory of Crop Genetics and Physiology/Jiangsu Key Laboratory of Crop Genomics and Molecular Breeding/Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou, 225009, China.
National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 300 Fenglin Road, Shanghai, 200032, China.
Plant J. 2020 Jul;103(1):140-153. doi: 10.1111/tpj.14715. Epub 2020 Apr 8.
The role of rice (Oryza sativa) COM1 in meiotic homologous recombination (HR) is well understood, but its part in somatic double-stranded break (DSB) repair remains unclear. Here, we show that for rice plants COM1 conferred tolerance against DNA damage caused by the chemicals bleomycin and mitomycin C, while the COM1 mutation did not compromise HR efficiencies and HR factor (RAD51 and RAD51 paralogues) localization to irradiation-induced DSBs. Similar retarded growth at the post-germination stage was observed in the com1-2 mre11 double mutant and the mre11 single mutant, while combined mutations in COM1 with the HR pathway gene (RAD51C) or classic non-homologous end joining (NHEJ) pathway genes (KU70, KU80, and LIG4) caused more phenotypic defects. In response to γ-irradiation, COM1 was loaded normally onto DSBs in the ku70 mutant, but could not be properly loaded in the MRE11 plant and in the wortmannin-treated wild-type plant. Under non-irradiated conditions, more DSB sites were occupied by factors (MRE11, COM1, and LIG4) than RAD51 paralogues (RAD51B, RAD51C, and XRCC3) in the nucleus of wild-type; protein loading of COM1 and XRCC3 was increased in the ku70 mutant. Therefore, quite differently to its role for HR in meiocytes, rice COM1 specifically acts in an alternative NHEJ pathway in somatic cells, based on the Mre11-Rad50-Nbs1 (MRN) complex and facilitated by PI3K-like kinases. NHEJ factors, not HR factors, preferentially load onto endogenous DSBs, with KU70 restricting DSB localization of COM1 and XRCC3 in plant somatic cells.
水稻（Oryza sativa）COM1 在减数分裂同源重组（HR）中的作用已被充分理解，但它在体细胞双链断裂（DSB）修复中的作用尚不清楚。在这里，我们表明，对于水稻植物，COM1 赋予了对化学物质博来霉素和丝裂霉素 C 引起的 DNA 损伤的耐受性，而 COM1 突变并不影响 HR 效率和 HR 因子（RAD51 和 RAD51 同源物）对辐射诱导的 DSB 的定位。在 com1-2 mre11 双突变体和 mre11 单突变体中观察到类似的发芽后阶段生长迟缓，而在 COM1 与 HR 途径基因（RAD51C）或经典非同源末端连接（NHEJ）途径基因（KU70、KU80 和 LIG4）的突变体中，表型缺陷更为严重。在对 γ 辐射的响应中，COM1 正常加载到 ku70 突变体中的 DSB 上，但不能在 MRE11 植物和wortmannin 处理的野生型植物中正常加载。在非照射条件下，在野生型核中，与 RAD51 同源物（RAD51B、RAD51C 和 XRCC3）相比，更多的 DSB 位点被 MRE11、COM1 和 LIG4 等因子占据；在 ku70 突变体中，COM1 和 XRCC3 的蛋白加载增加。因此，与在减数分裂细胞中的 HR 作用不同，水稻 COM1 特异性地在体细胞中的替代 NHEJ 途径中起作用，该途径基于 Mre11-Rad50-Nbs1（MRN）复合物，并由 PI3K 样激酶促进。NHEJ 因子而不是 HR 因子优先加载到内源性 DSB 上，KU70 限制 COM1 和 XRCC3 在植物体细胞中的 DSB 定位。
