College of Life Sciences, Capital Normal University, Beijing 100048, China.
Department of Biological Sciences, Mississippi State University, Mississippi State, MS 39762, USA.
Nucleic Acids Res. 2022 Jul 8;50(12):6820-6836. doi: 10.1093/nar/gkac469.
Nitric oxide (NO) is a key player in numerous physiological processes. Excessive NO induces DNA damage, but how plants respond to this damage remains unclear. We screened and identified an Arabidopsis NO hypersensitive mutant and found it to be allelic to TEBICHI/POLQ, encoding DNA polymerase θ. The teb mutant plants were preferentially sensitive to NO- and its derivative peroxynitrite-induced DNA damage and subsequent double-strand breaks (DSBs). Inactivation of TEB caused the accumulation of spontaneous DSBs largely attributed to endogenous NO and was synergistic to DSB repair pathway mutations with respect to growth. These effects were manifested in the presence of NO-inducing agents and relieved by NO scavengers. NO induced G2/M cell cycle arrest in the teb mutant, indicative of stalled replication forks. Genetic analyses indicate that Polθ is required for translesion DNA synthesis across NO-induced lesions, but not oxidation-induced lesions. Whole-genome sequencing revealed that Polθ bypasses NO-induced base adducts in an error-free manner and generates mutations characteristic of Polθ-mediated end joining. Our experimental data collectively suggests that Polθ plays dual roles in protecting plants from NO-induced DNA damage. Since Polθ is conserved in higher eukaryotes, mammalian Polθ may also be required for balancing NO physiological signaling and genotoxicity.
一氧化氮（NO）是许多生理过程中的关键参与者。过量的 NO 会导致 DNA 损伤，但植物如何应对这种损伤尚不清楚。我们筛选并鉴定了一个拟南芥 NO 超敏突变体，并发现它与编码 DNA 聚合酶θ的 TEBICHI/POLQ 等位。teb 突变体植物对 NO 及其衍生物过氧亚硝酸盐诱导的 DNA 损伤和随后的双链断裂（DSB）更敏感。TEB 的失活导致自发 DSB 的积累，主要归因于内源性 NO，并与 DSB 修复途径突变协同作用，对生长有影响。这些效应在存在 NO 诱导剂的情况下表现出来，并被 NO 清除剂缓解。NO 诱导 teb 突变体中的 G2/M 细胞周期停滞，表明复制叉停滞。遗传分析表明，Polθ 是跨 NO 诱导损伤进行转位 DNA 合成所必需的，但不是氧化诱导损伤。全基因组测序表明，Polθ 以无错误的方式绕过 NO 诱导的碱基加合物，并产生 Polθ 介导的末端连接特征性的突变。我们的实验数据表明，Polθ 在保护植物免受 NO 诱导的 DNA 损伤方面发挥双重作用。由于 Polθ 在高等真核生物中保守，哺乳动物 Polθ 也可能需要平衡 NO 的生理信号和遗传毒性。
