植物辐射旁效应诱导的遗传和表观遗传改变从不同的角度解释了低能离子束的诱变机制，赋予了低能离子生物学新的内涵。最近研究发现拟南芥辐射旁效应也可以诱导TGS（Transcriptional Gene Silencing）沉默元件的表观激活，并且和TGS序列的染色体定位有一定的关联。本项目在此基础上进一步研究染色体位置效应对辐射旁效应诱导TGS激活的影响及其特点、规律和分子机制。通过构建染色体不同位点的TGS-GUS报告基因转化群体，比较不同染色体定位的TGS-GUS对辐射旁效应的响应情况；进一步分析辐射前后TGS-GUS位点染色体DNA甲基化和组蛋白编码的状态改变，以及TGS调控基因功能缺失对辐射旁效应诱导TGS-GUS激活的影响及其对染色体位置的依赖性；综合以上实验数据，构建辐射旁效应诱导TGS表观激活的染色体位置效应数学模型，为充分理解低能离子束的诱变机制提供科学依据。

The radiation-induced bystander effects (RIBE) in plants provide a new insight into the mutagenesis of low-energy-ions. Recent researches have found that RIBE is epigenetic in nature, which suggests that epigenetic regulation may be involved in the biological effects of low-energy-ions. Our previous work shows that the TGS silenced loci can be transcriptionally activated through RIBE, and the process may be affected by the location of TGS loci in chromosome. In this proposal, we will further investigate the effects of chromosomal location on RIBE-induced TGS alleviation. First, a population transgenic for trans-TGS-GUS will be established, in which the TGS-GUS reporter gene will be stochastically located at various chromosomal loci. Then, the RIBE-mediated reactivation of TGS-GUS and corresponding epigenetic status will be measured in each independent line transgenic for TGS-GUS. The mechanisms underlying the epigenetic regulation of RIBE will be clarified using the mutant deficient in the TGS-regulating genes. Finally, a mathematic model of epigenetic regulation of RIBE-mediated alleviation of TGS will be established by integrating the above experimental data, which allows us to better understand the mechanisms underlying the mutagenesis of the low-energy-ions.