a Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, PR China.
b University of Science and Technology of China, Hefei 230026, PR China.
Radiat Res. 2019 Jun;191(6):556-565. doi: 10.1667/RR15314.1. Epub 2019 Apr 24.
Radiation-induced bystander effects (RIBE) entail a cascade of bystander signals produced by the hit cells to the neighboring cells to regulate various biological processes including DNA damage repair. However, there is little clarity regarding the effect of radiation-targeted volume (hit cell amount) on the DNA repair potential of the bystander cells. This is especially important to understand in the context of the whole organism, where the target usually consists of multiple types of cells/tissues. To address this question, model plant was locally irradiated, and the DNA repair potential of bystander root-tip cells was assessed based on their radioresistance to subsequent high-dose radiation, i.e. radioadaptive responses (RAR). We found that X-ray irradiation of the aerial parts (AP) of seedlings (5 Gy) initiated RAR in the root-tip cells, which exhibited an alleviated repression of root growth and root cell division, and reduced amount of DNA strand breaks. We also observed an improvement in the repair efficiency of the homologous recombination (HR) and non-homologous end joining (NHEJ) pathways in the bystander root tip cells. We further expanded the X-ray targeted volume to include the aerial parts with upper parts of the primary root and compared it with X-ray irradiated aerial parts alone. Comparative analysis revealed that RAR for these end points either disappeared or decreased; specifically, the repair efficiency of HR was significantly reduced, indicating that radiation-targeted volume negatively modulates the bystander DNA repair potential. In contrast, X-ray irradiation of upper part of the primary root alone did not induce RAR of the root tip cells. Thus, we propose that additional X-ray irradiation of upper part of the primary root reduces the bystander DNA repair potential, possibly by selectively disturbing the transport of bystander signals responsible for HR repair.
辐射诱导的旁观者效应（RIBE）涉及到一系列由受照射细胞产生的旁观者信号，这些信号调节各种生物学过程，包括 DNA 损伤修复。然而，对于辐射靶向体积（受照射细胞数量）对旁观者细胞的 DNA 修复潜力的影响，目前还不太清楚。在整个生物体的背景下，这一点尤其重要，因为目标通常由多种类型的细胞/组织组成。为了解决这个问题，我们对模式植物进行了局部照射，并根据后续高剂量辐射（即辐射适应性反应，RAR）对旁观者根尖细胞的放射抗性来评估其 DNA 修复潜力。我们发现，对 幼苗的地上部分（AP）进行 X 射线照射（5Gy）会在根尖细胞中引发 RAR，表现为根生长和根细胞分裂的抑制减轻，以及 DNA 链断裂减少。我们还观察到旁观者根尖细胞中同源重组（HR）和非同源末端连接（NHEJ）途径的修复效率提高。我们进一步扩大了 X 射线靶向体积，将其包括地上部分和主根的上部，并将其与仅对地上部分进行 X 射线照射进行了比较。对比分析表明，对于这些终点，RAR 要么消失，要么减少；具体来说，HR 的修复效率显著降低，表明辐射靶向体积负调节旁观者 DNA 修复潜力。相比之下，仅对主根上部进行 X 射线照射不会诱导根尖细胞的 RAR。因此，我们提出，主根上部的额外 X 射线照射会降低旁观者 DNA 修复潜力，可能是通过选择性干扰负责 HR 修复的旁观者信号的传递。
