Ocean College, Zhejiang University, Zhoushan, China.
Department of Molecular Genetics and Microbiology, Duke University, Durham, North Carolina, United States of America.
PLoS Genet. 2023 Jan 26;19(1):e1010590. doi: 10.1371/journal.pgen.1010590. eCollection 2023 Jan.
Although homologous recombination between transposable elements can drive genomic evolution in yeast by facilitating chromosomal rearrangements, the details of the underlying mechanisms are not fully clarified. In the genome of the yeast Saccharomyces cerevisiae, the most common class of transposon is the retrotransposon Ty1. Here, we explored how Cas9-induced double-strand breaks (DSBs) directed to Ty1 elements produce genomic alterations in this yeast species. Following Cas9 induction, we observed a significant elevation of chromosome rearrangements such as deletions, duplications and translocations. In addition, we found elevated rates of mitotic recombination, resulting in loss of heterozygosity. Using Southern analysis coupled with short- and long-read DNA sequencing, we revealed important features of recombination induced in retrotransposons. Almost all of the chromosomal rearrangements reflect the repair of DSBs at Ty1 elements by non-allelic homologous recombination; clustered Ty elements were hotspots for chromosome rearrangements. In contrast, a large proportion (about three-fourths) of the allelic mitotic recombination events have breakpoints in unique sequences. Our analysis suggests that some of the latter events reflect extensive processing of the broken ends produced in the Ty element that extend into unique sequences resulting in break-induced replication. Finally, we found that haploid and diploid strain have different preferences for the pathways used to repair double-stranded DNA breaks. Our findings demonstrate the importance of DNA lesions in retrotransposons in driving genome evolution.
虽然转座元件之间的同源重组可以通过促进染色体重排来推动酵母的基因组进化,但其中的具体机制尚未完全阐明。在酵母 Saccharomyces cerevisiae 的基因组中,最常见的转座元件是反转录转座子 Ty1。在这里,我们探讨了 Cas9 诱导的双链断裂 (DSB) 靶向 Ty1 元件如何在这种酵母物种中产生基因组改变。在 Cas9 诱导后,我们观察到明显增加的染色体重排,如缺失、重复和易位。此外,我们发现有丝分裂重组率升高,导致杂合性丧失。通过 Southern 分析结合短读长和长读长 DNA 测序,我们揭示了反转录转座子诱导的重组的重要特征。几乎所有的染色体重排都反映了 Ty1 元件处 DSB 的非等位同源重组修复;聚类 Ty 元件是染色体重排的热点。相比之下,相当大比例(约四分之三)的等位有丝分裂重组事件的断点位于独特序列中。我们的分析表明,这些事件中的一些反映了 Ty 元件中产生的断裂末端的广泛处理,这些末端延伸到独特序列中,导致断裂诱导复制。最后,我们发现,单倍体和二倍体菌株对修复双链 DNA 断裂的途径有不同的偏好。我们的研究结果表明,反转录转座子中的 DNA 损伤在推动基因组进化方面起着重要作用。