Botanical Institute, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Nat Protoc. 2022 May;17(5):1332-1358. doi: 10.1038/s41596-022-00686-7. Epub 2022 Apr 6.
The rise of the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein (Cas) system has made it possible to induce double-strand breaks at almost any desired target site in the genome. In plant somatic cells, double-strand breaks are predominantly repaired by the error-prone nonhomologous end-joining pathway, which can lead to mutations at the break site upon repair. So far, it had only been possible to induce genomic changes of up to a few hundred kilobases in plants utilizing this mechanism. However, by combining the highly efficient Staphylococcus aureus Cas9 (SaCas9) with an egg-cell-specific promoter to facilitate heritable mutations, chromosomal rearrangements in the Mb range, such as inversion and translocations, were obtained in Arabidopsis thaliana recently. Here we describe the chromosome-engineering protocol used to generate these heritable chromosomal rearrangements in A. thaliana. The protocol is based on Agrobacterium-mediated transformation of A. thaliana with transfer DNA constructs containing SaCas9, which is driven by an egg-cell-specific promoter, and two guide RNAs that have been preselected based on their cutting efficiency. In the T1 generation, primary transformants are selected and, if required, analyzed by Droplet Digital PCR and propagated. In the following generations, junction-specific PCR screenings are carried out until plants that carry the rearrangement homozygously are identified. Using this protocol, overall rearrangement frequencies range between 0.03% and 0.5%, depending on the type of rearrangement. In total, it takes about 1 year to establish homozygous lines.
CRISPR-Cas 系统的出现使得在基因组的几乎任何所需目标位点诱导双链断裂成为可能。在植物体细胞中,双链断裂主要通过易错的非同源末端连接途径进行修复,该途径在修复时会导致断裂部位发生突变。到目前为止,利用这种机制只能在植物中诱导多达几百千碱基对的基因组变化。然而,最近通过将高效的金黄色葡萄球菌 Cas9(SaCas9)与卵母细胞特异性启动子结合,以促进可遗传的突变,在拟南芥中获得了 Mb 范围内的染色体重排,如倒位和易位。在这里,我们描述了用于在拟南芥中产生这些可遗传染色体重排的染色体工程方案。该方案基于含有 SaCas9 的转移 DNA 构建体的农杆菌介导的拟南芥转化,该构建体由卵母细胞特异性启动子驱动,并且两个向导 RNA 是根据其切割效率预先选择的。在 T1 代中,选择初级转化体,如果需要,通过液滴数字 PCR 进行分析并进行繁殖。在随后的几代中,进行接头特异性 PCR 筛选,直到鉴定出携带重排的纯合植株。使用该方案,总体重排频率在 0.03%到 0.5%之间,具体取决于重排的类型。总共需要大约 1 年的时间才能建立纯合系。