Academic literature on the topic 'DNA-free gene editing'

Genome-editing technologies based on the CRISPR (clustered regularly interspaced short palindromic repeat) system have been widely used in plants to investigate gene function and improve crop traits. The recently developed DNA-free delivery methods and precise base-editing systems provide new opportunities for plant genome engineering. In this review, we describe the novel DNA-free genome-editing methods in plants. These methods reduce off-target effects and may alleviate regulatory concern about genetically modified plants. We also review applications of base-editing systems, which are highly effective in generating point mutations and are of great value for introducing agronomically valuable traits. Future perspectives for DNA-free editing and base editing are also discussed.

Abstract Transgene residuals in edited plants affect genetic analysis, pose off-target risks, and cause regulatory concerns. Several strategies have been developed to efficiently edit target genes without leaving any transgenes in plants. Some approaches directly address this issue by editing plant genomes with DNA-free reagents. On the other hand, DNA-based techniques require another step for ensuring plants are transgene-free. Fluorescent markers, pigments, and chemical treatments have all been employed as tools to distinguish transgenic plants from transgene-free plants quickly and easily. Moreover, suicide genes have been used to trigger self-elimination of transgenic plants, greatly improving the efficiency of isolating the desired transgene-free plants. Transgenes can also be excised from plant genomes using site-specific recombination, transposition or gene editing nucleases, providing a strategy for editing asexually produced plants. Finally, haploid induction coupled with gene editing may make it feasible to edit plants that are recalcitrant to transformation. Here, we evaluate the strengths and weaknesses of recently developed approaches for obtaining edited plants without transgene residuals.

Primary endothelial cells (ECs), especially human umbilical vein endothelial cells (HUVECs), are broadly used in vascular biology. Gene editing of primary endothelial cells is known to be challenging, due to the low DNA transfection efficiency and the limited proliferation capacity of ECs. We report the establishment of a highly efficient and selection-free CRISPR gene editing approach for primary endothelial cells (HUVECs) with ribonucleoprotein (RNP) complex. We first optimized an efficient and cost-effective protocol for messenger RNA (mRNA) delivery into primary HUVECs by nucleofection. Nearly 100% transfection efficiency of HUVECs was achieved with EGFP mRNA. Using this optimized DNA-free approach, we tested RNP-mediated CRISPR gene editing of primary HUVECs with three different gRNAs targeting the HIF1A gene. We achieved highly efficient (98%) and biallelic HIF1A knockout in HUVECs without selection. The effects of HIF1A knockout on ECs’ angiogenic characteristics and response to hypoxia were validated by functional assays. Our work provides a simple method for highly efficient gene editing of primary endothelial cells (HUVECs) in studies and manipulations of ECs functions.

Abstract CRISPR/Cas9-mediated gene editing of stem cells and primary cell types has several limitations for clinical applications. The direct delivery of ribonucleoprotein (RNP) complexes consisting of Cas9 nuclease and guide RNA (gRNA) has improved DNA- and virus-free gene modifications, but it does not enable the essential enrichment of the gene-edited cells. Here, we established a protocol for the fluorescent labeling and delivery of CRISPR/Cas9–gRNA RNP in primary human hematopoietic stem and progenitor cells (HSPCs) and induced pluripotent stem cells (iPSCs). As a proof of principle for genes with low-abundance transcripts and context-dependent inducible expression, we successfully deleted growth arrest and DNA-damage-inducible β (GADD45B). We found that GADD45B is indispensable for DNA damage protection and survival in stem cells. Thus, we describe an easy and efficient protocol of DNA-free gene editing of hard-to-target transcripts and enrichment of gene-modified cells that are generally difficult to transfect.

Genome-editing (GE) is having a tremendous influence around the globe in the life science community. Among its versatile uses, the desired modifications of genes, and more importantly the transgene (DNA)-free approach to develop genetically modified organism (GMO), are of special interest. The recent and rapid developments in genome-editing technology have given rise to hopes to achieve global food security in a sustainable manner. We here discuss recent developments in CRISPR-based genome-editing tools for crop improvement concerning adaptation, opportunities, and challenges. Some of the notable advances highlighted here include the development of transgene (DNA)-free genome plants, the availability of compatible nucleases, and the development of safe and effective CRISPR delivery vehicles for plant genome editing, multi-gene targeting and complex genome editing, base editing and prime editing to achieve more complex genetic engineering. Additionally, new avenues that facilitate fine-tuning plant gene regulation have also been addressed. In spite of the tremendous potential of CRISPR and other gene editing tools, major challenges remain. Some of the challenges are related to the practical advances required for the efficient delivery of CRISPR reagents and for precision genome editing, while others come from government policies and public acceptance. This review will therefore be helpful to gain insights into technological advances, its applications, and future challenges for crop improvement.

The current genome editing system Clustered Regularly Interspaced Short Palindromic Repeats Cas9 (CRISPR/Cas9) has already confirmed its proficiency, adaptability, and simplicity in several plant-based applications. Together with the availability of a vast amount of genome data and transcriptome data, CRISPR/Cas9 presents a massive opportunity for plant breeders and researchers. The successful delivery of ribonucleoproteins (RNPs), which are composed of Cas9 enzyme and a synthetically designed single guide RNA (sgRNA) and are used in combination with various transformation methods or lately available novel nanoparticle-based delivery approaches, allows targeted mutagenesis in plants species. Even though this editing technique is limitless, it has still not been employed in many plant species to date. Chickpea is the second most crucial winter grain crop cultivated worldwide; there are currently no reports on CRISPR/Cas9 gene editing in chickpea. Here, we selected the 4-coumarate ligase (4CL) and Reveille 7 (RVE7) genes, both associated with drought tolerance for CRISPR/Cas9 editing in chickpea protoplast. The 4CL represents a key enzyme involved in phenylpropanoid metabolism in the lignin biosynthesis pathway. It regulates the accumulation of lignin under stress conditions in several plants. The RVE7 is a MYB transcription factor which is part of regulating circadian rhythm in plants. The knockout of these selected genes in the chickpea protoplast using DNA-free CRISPR/Cas9 editing represents a novel approach for achieving targeted mutagenesis in chickpea. Results showed high-efficiency editing was achieved for RVE7 gene in vivo compared to the 4CL gene. This study will help unravel the role of these genes under drought stress and understand the complex drought stress mechanism pathways. This is the first study in chickpea protoplast utilizing CRISPR/Cas9 DNA free gene editing of drought tolerance associated genes.

AbstractGene editing is a powerful tool for genome and cell engineering. Exemplified by CRISPR–Cas, gene editing could cause DNA damage and trigger DNA repair processes that are often error-prone. Such unwanted mutations and safety concerns can be exacerbated when altering long sequences. Here we couple microbial single-strand annealing proteins (SSAPs) with catalytically inactive dCas9 for gene editing. This cleavage-free gene editor, dCas9–SSAP, promotes the knock-in of long sequences in mammalian cells. The dCas9–SSAP editor has low on-target errors and minimal off-target effects, showing higher accuracy than canonical Cas9 methods. It is effective for inserting kilobase-scale sequences, with an efficiency of up to approximately 20% and robust performance across donor designs and cell types, including human stem cells. We show that dCas9–SSAP is less sensitive to inhibition of DNA repair enzymes than Cas9 references. We further performed truncation and aptamer engineering to minimize its size to fit into a single adeno-associated-virus vector for future application. Together, this tool opens opportunities towards safer long-sequence genome engineering.

Abstract Genome editing technology is important for plant science and crop breeding. Genome-edited plants prepared using general CRISPR-Cas9 methods usually contain foreign DNA, which is problematic for the production of genome-edited transgene-free plants for vegetative propagation or highly heterozygous hybrid cultivars. Here, we describe a method for highly efficient targeted mutagenesis in Nicotiana benthamiana through the expression of Cas9 and single-guide (sg)RNA using a potato virus X (PVX) vector. Following Agrobacterium-mediated introduction of virus vector cDNA, >60% of shoots regenerated without antibiotic selection carried targeted mutations, while ≤18% of shoots contained T-DNA. The PVX vector was also used to express a base editor consisting of modified Cas9 fused with cytidine deaminase to introduce targeted nucleotide substitution in regenerated shoots. We also report exogenous DNA-free genome editing by mechanical inoculation of virions comprising the PVX vector expressing Cas9. This simple and efficient virus vector-mediated delivery of CRISPR-Cas9 could facilitate transgene-free gene editing in plants.

Global agricultural productivity, farm incomes, and food security will all be impacted by climate change. Grape (Vitis vinifera L.) is one of the world's most commercially significant fruit crops, and it is extensively cultivated for fruits, juice, and, most importantly, wine. Scientific evidence sharply states that climate change represents a dominant challenge for viticulture in the upcoming decades. Agriculture and farming around the world are highly depended on crops that produce food and fiber for humans, either directly or indirectly through livestock. Modern technology has improved agricultural operations over the last two centuries, complementing traditional plant breeding approaches to improve crop productivity and quality. Combining synthetic tools and traditional breeding into genomics-based breeding is a novel way to get over the limitations of traditional breeding. Genome editing offers the potential to speed up basic research and plant breeding by allowing for quick, accurate, and targeted genome editing. The revolutionary CRISPR-Cas system offers enormous potential for editing gene expression for crop improvement and food production. Genome editing is a powerful way to find and precisely locate a specific region inside a genome, then edit the targeted regions for a variety of applications. Unlike traditional transgenic technology, which randomly introduces genetic components into a genome, genomic editing operates on a specific genome sequence inside the genome. The risks of altering genomes via genome-editing technologies are considerably less than those associated with genetically modified (GM) crops since most edits typically affect a few nucleotides leading to changes similar to those found in naturally occurring populations. There is no way to tell the difference between a 'naturally occurring' mutation and a gene edit after the genomic-editing agents have separated. This DNA-free RNP delivery approach is promising for plant breeding since the resulting edited crops are likely falling outside of GMO regulation. Consequently, DNA-free genome editing is a game-changing technique that allow for faster and more precise crop development. In this study, we described a successful knockout of a green fluorescent protein (GFP) reporter gene, that is already integrated into the grape genome with a single copy, in V. vinifera "Sultana" by direct delivery of RNPs into protoplast. We demonstrated the use of this powerful new tool in targeted knockout of a gene settled in the grape genome. By following the loss of the GFP fluorescence signal, we were able to observe the cells that had endured targeted mutations as a result of CRISPR/ Cas9 activity. In addition, we presented examples of the various types of indels obtained by Cas9-mediated cleavage of the GFP gene, guided by two independent sgRNAs. The application of the CRISPR/Cas9 RNP system enables the generation of grape plants engineered by DNA-free gene editing. Eventually, we provided an optimized protocol to target important native genes in the grape plant in the future. In this study for the first time, we managed to achieve whole plants regenerated from DNA-free genome edited protoplasts. Monitoring the protoplast to whole plant developmental stages demonstrated that regenerated plantlets derived from gene-edited protoplasts exhibited a normal phenotype concerning leaf shape, color and growth habits compared to wild-type plants. Here an efficient protocol has been presented for foreign DNA-free CRISPR/Cas9 mediated gene editing in Vitis vinifera Sultana including detailed protoplast-to-plant steps.

Clustered regularly interspaced short palindromic repeats/CRISPR-associated system (CRISPR/Cas) is a powerful gene editing tool that can introduce double-strand breaks (DSBs) at precise target sites in genomic DNA. In mammalian cells, the CRISPR/Cas-generated DSBs can be repaired by either template-free error-prone end joining (e.g., non-homologous end joining/microhomology-mediated end joining [NHEJ]/[MMEJ]) or templated error-free homology-directed repair (HDR) pathways. CRISPR/Cas with NHEJ/MMEJ DNA repair results in various length insertions/deletion mutations (indels), which can cause frameshift mutations leading to a stop codon and subsequent gene-specific knockout (i.e., loss of function). In contrast, CRISPR/Cas with HDR DNA repair, utilizing an exogenous repair template harboring specific nucleotide (nt) changes, can be employed to intentionally edit out or introduce mutations or insertions at specific genomic sites (i.e., targeted gene knock-in). This review provides an overview of HDR-based gene-targeting strategies to facilitate the knock-in process, including improving gRNA cleavage efficiency, optimizing HDR efficacy, decreasing off-target effects, suppressing NHEJ/MMEJ activity, and thus expediting the screening of CRISPR/Cas-edited clonal cells.