Cytosine base editors (CBEs) are great additions to the expanding genome editing toolbox. To improve C‐to‐T base editing in plants, we first compared seven cytidine deaminases in the BE3‐like configuration in rice. We found A3A/Y130F‐CBE_V01 resulted in the highest C‐to‐T base editing efficiency in both rice and
- NSF-PAR ID:
- 10388215
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Plant Biotechnology Journal
- Volume:
- 19
- Issue:
- 10
- ISSN:
- 1467-7644
- Page Range / eLocation ID:
- p. 2052-2068
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Abstract Cytosine base editors (CBEs) are promising tools for precise genome editing in plants. It is important to investigate potential off-target effects of an efficient CBE at the genome and transcriptome levels in a major crop. Based on comparison of five cytidine deaminases and two different promoters for expressing sgRNAs, we tested a highly efficient A3A/Y130F-BE3 system for efficient C-to-T base editing in tomato (Solanum lycopersicum). We then conducted whole-genome sequencing (WGS) of four base-edited tomato plants, three GFP-expressing control plants, and two wild-type (WT) plants. The sequencing depths ranged from 25X to 49X with read mapping rates above 97%. No sgRNA-dependent off-target mutations were detected. Our data show an average of ∼1000 single nucleotide variations (SNVs) and ∼100 insertions and deletions (indels) per GFP control plant. Base-edited plants had on average elevated levels of SNVs (∼1250) and indels (∼300) per plant. On average, about 200 more C-to-T (G-to-A) mutations were found in a base-edited plant than a GFP control plant, suggesting some level of sgRNA-independent off-target effects, though the difference is not statistically significant. We also conducted RNA sequencing (RNA-seq) of the same four base-edited plants and three GFP control plants. An average of ∼200 RNA SNVs was discovered per plant for either base-edited or GFP control plants. Furthermore, no specific enrichment of C-to-U mutations can be found in the base-edited plants. Hence, we cannot find any evidence for bona fide off-target mutations by A3A/Y130F-BE3 at the transcriptome level.more » « less
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Cytosine base editors (CBEs) enable efficient cytidine-to-thymidine (C-to-T) substitutions at targeted loci without double-stranded breaks. However, current CBEs edit all Cs within their activity windows, generating undesired bystander mutations. In the most challenging circumstance, when a bystander C is adjacent to the targeted C , existing base editors fail to discriminate them and edit both Cs. To improve the precision of CBE, we identified and engineered the human APOBEC3G (A3G) deaminase; when fused to the Cas9 nickase, the resulting A3G-BEs exhibit selective editing of the second C in the 5′-C C -3′ motif in human cells. Our A3G-BEs could install a single disease-associated C-to-T substitution with high precision. The percentage of perfectly modified alleles is more than 6000-fold for disease correction and more than 600-fold for disease modeling compared with BE4max. On the basis of the two-cell embryo injection method and RNA sequencing analysis, our A3G-BEs showed minimum genome- and transcriptome-wide off-target effects, achieving high targeting fidelity.more » « less
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Abstract Adenine base editors (ABEs) are valuable, precise genome editing tools in plants. In recent years, the highly promising ADENINE BASE EDITOR8e (ABE8e) was reported for efficient A-to-G editing. However, compared to monocots, comprehensive off-target analyses for ABE8e are lacking in dicots. To determine the occurrence of off-target effects in tomato (Solanum lycopersicum), we assessed ABE8e and a high-fidelity version, ABE8e-HF, at 2 independent target sites in protoplasts, as well as stable T0 lines. Since ABE8e demonstrated higher on-target efficiency than ABE8e-HF in tomato protoplasts, we focused on ABE8e for off-target analyses in T0 lines. We conducted whole-genome sequencing (WGS) of wild-type (WT) tomato plants, green fluorescent protein (GFP)–expressing T0 lines, ABE8e-no-gRNA control T0 lines, and edited T0 lines. No guide RNA (gRNA)–dependent off-target edits were detected. Our data showed an average of approximately 1,200 to 1,500 single-nucleotide variations (SNVs) in either GFP control plants or base-edited plants. Also, no specific enrichment of A-to-G mutations were found in base-edited plants. We also conducted RNA sequencing (RNA-seq) of the same 6 base-edited and 3 GFP control T0 plants. On average, approximately 150 RNA–level SNVs were discovered per plant for either base-edited or GFP controls. Furthermore, we did not find enrichment of a TA motif on mutated adenine in the genomes and transcriptomes in base-edited tomato plants, as opposed to the recent discovery in rice (Oryza sativa). Hence, we could not find evidence for genome- and transcriptome-wide off-target effects by ABE8e in tomato.
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Abstract Phytopathogenic bacteria play important roles in plant productivity, and developments in gene editing have potential for enhancing the genetic tools for the identification of critical genes in the pathogenesis process. CRISPR-based genome editing variants have been developed for a wide range of applications in eukaryotes and prokaryotes. However, the unique mechanisms of different hosts restrict the wide adaptation for specific applications. Here, CRISPR-dCas9 (dead Cas9) and nCas9 (Cas9 nickase) deaminase vectors were developed for a broad range of phytopathogenic bacteria. A gene for a dCas9 or nCas9, cytosine deaminase CDA1, and glycosylase inhibitor fusion protein (cytosine base editor, or CBE) was applied to base editing under the control of different promoters. Results showed that the RecA promoter led to nearly 100% modification of the target region. When residing on the broad host range plasmid pHM1, CBERecApis efficient in creating base edits in strains of
Xanthomonas ,Pseudomonas ,Erwinia andAgrobacterium . CBE based on nCas9 extended the editing window and produced a significantly higher editing rate inPseudomonas . Strains with nonsynonymous mutations in test genes displayed expected phenotypes. By multiplexing guide RNA genes, the vectors can modify up to four genes in a single round of editing. Whole-genome sequencing of base-edited isolates ofXanthomonas oryzae pv.oryzae revealed guide RNA-independent off-target mutations. Further modifications of the CBE, using a CDA1 variant (CBERecAp-A) reduced off-target effects, providing an improved editing tool for a broad group of phytopathogenic bacteria. -
Summary Using genetic resistance against bacterial blight (BB) caused by
Xanthomonas oryzae pathovaroryzae (Xoo ) is a major objective in rice breeding programmes. Prime editing (PE) has the potential to create novel germplasm againstXoo . Here, we use an improved prime‐editing system to implement two new strategies for BB resistance. Knock‐in of TAL effector binding elements (EBE) derived from the BB susceptible geneSWEET14 into the promoter of a dysfunctional executorR genexa23 reaches 47.2% with desired edits including biallelic editing at 18% in T0generation that enables an inducible TALE‐dependent BB resistance. Editing the transcription factor TFIIA geneTFIIAγ5 required for TAL effector‐dependent BB susceptibility recapitulates the resistance ofxa5 at an editing efficiency of 88.5% with biallelic editing rate of 30% in T0generation. The engineered loci provided resistance against multipleXoo strains in T1generation. Whole‐genome sequencing detected noOsMLH1dn ‐associated random mutations and no off‐target editing demonstrating high specificity of this PE system. This is the first‐ever report to use PE system to engineer resistance against biotic stress and to demonstrate knock‐in of 30‐nucleotides cis‐regulatory element at high efficiency. The new strategies hold promises to fend rice off the evolvingXoo strains and protect it from epidemics.