![]() ![]() Single gRNA CRISPR-Cas9 systems normally generate SNP or short indel mutations at target sites, which can be detected by time-consuming and laborious methods, like DNA sequencing or PCR–RFLP if the mutation destroys a restriction enzyme site. In addition, the generated mutations are often somatic and rarely transmitted to the next generation. However, the CRISPR/Cas9 system-directed gene-editing efficiency is much lower in Arabidopsis compared to other plant species, probably because the Arabidopsis gene transformation method does not require a tissue regeneration process, which is usually applied to most plant species. The early versions usually encode a single gRNA driven by a Pol III promoter and a Cas9 gene driven by the 35S promoter (Shan et al. 2013).Ī number of CRISPR/Cas9 systems have been developed and successfully applied to edit genes in Arabidopsis (Ma et al. The latter process often leads to insertions, deletions, or substitutions at the target sites (Mali et al. Then, DSB is repaired through either an error-free homologous recombination mechanism or an error-prone non-homologous end-joining pathway. After being expressed in plants, Cas9 is introduced to the genomic site that is base-paired with the gRNA spacer, binds to its downstream protospacer adjacent motif (PAM) with a consensus sequence of NGG, and creates a double-strand break (DSB) at a site ~ 3 bp upstream of PAM (Jinek et al. It consists of two components, an endonuclease Cas9 and a synthetic guide RNA (gRNA) harboring a 20-nt spacer and a 76-nt Cas9-binding scaffold. 2012 Fineran and Charpentier 2012 Gasiunas et al. ![]() The CRISPR/Cas9 system is derived from the type II CRISPR adaptive immune system in Streptococcus pyogenes, which detects and degrades invasive DNAs from bacteriophages and plasmids (Jinek et al. Today, the RNA-guided nuclease complex, the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9 (Cas9), is the most powerful and widely used tool to edit genes in diverse organisms due to its high efficiency and great specificity (Jinek et al. ![]() Therefore, there still is a large need to create gene knockout mutants in Arabidopsis and gene-editing technologies provide powerful tools to fulfil this imperative requirement (Liu et al. Moreover, T-DNA favors inserting into the regions of transcriptional initiation and polyadenylation, which usually results in a partial suppression of gene’s functions (Li et al. However, there are still 12% of Arabidopsis genes lacking T-DNA insertion and 8% genes with a single insertion in publically available T-DNA insertional mutant libraries (O’Malley and Ecker 2010 Kleinboelting et al. We propose that it could be applied to other genes in Arabidopsis, and it might have the potential to edit genes in other plant species as well.Ĭollections of T-DNA insertional mutants have made vital contributions to determining functions of Arabidopsis genes. We conclude that the rice PTG/Cas9 system is an efficient, easy, and rapid tool to edit genes in Arabidopsis. We established a standard and reliable protocol to generate stable inherited deletion mutants in 2–3 generations along with simple PCR screening methods. We further targeted five other genes using the same procedure and achieved homozygous Cas9-free mutants with large deletions for all genes within three generations. Inheritable homozygous ptox mutants without Cas9 gene can be obtained earliest at T2 generation. After a self-cross propagation, 60% of T1 chimeric plants were able to produce homozygous, heterozygous, or bi-allelic ptox offsprings. At T1 generation, 24.4% of transgenic plants were chimeric with PCR-detectable deletions in PTOX locus, but no homozygous mutant was found, indicating that gene editing occurred predominantly in somatic cells. We constructed a PTOX–PTG/Cas9 system with five gRNAs and introduced it into Arabidopsis. The PTG/Cas9 system has a great potential in generating large deletions detectable by PCR, which greatly simplifies the laborious work of mutant screening. To develop an easy and robust method for creating genetically stable and easily detectable Arabidopsis mutants, we adopted the polycistronic tRNA–gRNA CRISPR/Cas9 (PTG/Cas9) system, a multiplex gene-editing tool in rice, with PTOX as the reporter gene. ![]()
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