植物DNA修复相关基因对突变率及重组率的影响

Mutation and recombination are arguably the most important source of all biological variation, which provide raw materials for evolution, as well as contribute to genetic or somatic diseases. Recombination not only reshuffles genetic variations and generate new allelic combinations, but also have a possible more crucial role is in DNA repairing process. Such a process was also found to be mutagenic, therefore, genes involved in the repairing process could have a determining role in the mutation rate as well as the recombination rate. However, previous assessment of those genes only incorporate limited species (e.g. yeast) and limited sites (by using loci carrying reporter genes). Whether they have a genome-wide influence on other species remain largely unknown. Here, we choose two genes MSH2 and FANCM, both encoding components involved in DNA repair system. By incorporating CRISPR/Cas9 system and next-generation sequencing technology, we could estimate the genome-wide mutation and recombination rate of the deficient mutants in model plant Arabidopsis thaliana and rice. This would give the first directly assessment in the whole genome scale in plants, to our knowledge, of the impact of those genes. We should be able to answer the question whether the distribution of mutation and recombination would be distorted in those mutants. In addition, by further testing the relationship between mutation and heterozygosity, we should be closer to the inner mechanisms which drive the related processes.

突变和重组过程是生物体所有生物变异的根本来源，其为演化提供了原始材料，是很多表型与疾病产生的根本原因。而DNA修复过程又是突变与重组产生的重要途径，在其产生的过程当中扮演着重要的角色。然而对DNA修复相关的研究基本只局限个别物种以及有限的位点，缺少全基因组尺度的证据。本研究拟选取两个与修复过程密切相关的重要基因，以模式植物拟南芥和水稻作为研究对象，利用已有的或者CRISPR/Cas9技术敲除得到的相关DNA修复基因缺陷突变体，通过高通量测序技术在全基因组尺度精确评估相关基因缺失后的突变率以及重组率。通过与正常情况下突变与重组的分布情况进行比较，揭示修复系统异常情况下突变以及重组的分布规律是否会产生变化。除此之外，我们将进一步验证在这些突变体中异质性对于突变率的影响是否依然存在，从而确定异质性与修复系统是否具有一定的关联，为解答异质性作用的阶段以及作用机制打下基础。

突变是生物多样性的根本来源，其为演化提供了原始材料，也是大部分表型变异形成的根源。DNA修复过程与突变产生息息相关，但目前为止相关研究还只局限在个别物种的有限位点，缺少全基因组尺度的系统评估。本项目通过对拟南芥和水稻中参与错配修复过程的MSH2与MSH6基因突变体展开详细考察，表明错配修复基因的缺失会造成突变率相比于野生型上升20-100倍；MSH2基因主要倾向于修复C>T/G>A类型突变，而MSH6基因则倾向于修复C>A/G>T类型的突变，而且发生区域的偏好性也存在显著的区别。该结果一方面表明虽然重组过程能够一定程度上减少有害突变的积累，但在修复系统缺陷的情况下，大规模的突变产生还是会对植物生长发育过程产生较大的影响；另一方面不同修复基因的角色既存在冗余又存在各自独特的偏好性，其在植物当中保持着保守的功能，对于维持植物基因组稳定性扮演了极为重要的角色。相关结果为进一步研究植物突变调控机制打下了基础，也为寻找所有物种当中突变重组的普适性规律提供了线索。