A review of CRISPR associated genome engineering: application, advances and future prospects of genome targeting tool for crop improvement

Leveraging the sugarcane CRISPR/Cas9 technique for genetic improvement of non-cultivated grasses

Under changing climatic scenarios, grassland conservation and development have become imperative to impart functional sustainability to their ecosystem services. These goals could be effectively and efficiently achieved with targeted genetic improvement of native grass species. To the best of our literature search, very scant research findings are available pertaining to gene editing of non-cultivated grass species (switch grass, wild sugarcane, Prairie cordgrass, Bermuda grass, Chinese silver grass, etc.) prevalent in natural and semi-natural grasslands. Thus, to explore this novel research aspect, this study purposes that gene editing techniques employed for improvement of cultivated grasses especially sugarcane might be used for non-cultivated grasses as well. Our hypothesis behind suggesting sugarcane as a model crop for genetic improvement of non-cultivated grasses is the intricacy of gene editing owing to polyploidy and aneuploidy compared to other cultivated grasses (rice, wheat, barley, maize, etc.). Another reason is that genome editing protocols in sugarcane (x = 10-13) have been developed and optimized, taking into consideration the high level of genetic redundancy. Thus, as per our knowledge, this review is the first study that objectively evaluates the concept and functioning of the CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 technique in sugarcane regarding high versatility, target specificity, efficiency, design simplicity, and multiplexing capacity in order to explore novel research perspectives for gene editing of non-cultivated grasses against biotic and abiotic stresses. Additionally, pronounced challenges confronting sugarcane gene editing have resulted in the development of different variants (Cas9, Cas12a, Cas12b, and SpRY) of the CRISPR tool, whose technicalities have also been critically assessed. Moreover, different limitations of this technique that could emerge during gene editing of non-cultivated grass species have also been highlighted.

Antisense RNA (asRNA) technology: the concept and applications in crop improvement and sustainable agriculture

Antisense RNA (asRNA) technology is a method used to silence genes and inhibit their expression. Gene function relies on expression, which follows the central dogma of molecular biology. The use of asRNA can regulate gene expression by targeting specific mRNAs, which can result in changes in phenotype, disease resistance, and other traits associated with protein expression profiles. This technology uses short, single-stranded oligonucleotide strands that are complementary to the targeted mRNA. Manipulating and regulating protein expression during its translation can either knock out or knock down the expression of a gene of interest. Therefore, functional genomics can benefit from this technology since it allows for the regulation of protein expression. In this review, we discuss the concept, and applications of asRNA technology which include delaying ripening, prolonging shelf life, biofortification, and increasing biotic and abiotic resistance among others in crop improvement and sustainable agriculture.

CRISPR genome editing using computational approaches: A survey

Clustered regularly interspaced short palindromic repeats (CRISPR)-based gene editing has been widely used in various cell types and organisms. To make genome editing with Clustered regularly interspaced short palindromic repeats far more precise and practical, we must concentrate on the design of optimal gRNA and the selection of appropriate Cas enzymes. Numerous computational tools have been created in recent years to help researchers design the best gRNA for Clustered regularly interspaced short palindromic repeats researches. There are two approaches for designing an appropriate gRNA sequence (which targets our desired sites with high precision): experimental and predicting-based approaches. It is essential to reduce off-target sites when designing an optimal gRNA. Here we review both traditional and machine learning-based approaches for designing an appropriate gRNA sequence and predicting off-target sites. In this review, we summarize the key characteristics of all available tools (as far as possible) and compare them together. Machine learning-based tools and web servers are believed to become the most effective and reliable methods for predicting on-target and off-target activities of Clustered regularly interspaced short palindromic repeats in the future. However, these predictions are not so precise now and the performance of these algorithms -especially deep learning one's-depends on the amount of data used during training phase. So, as more features are discovered and incorporated into these models, predictions become more in line with experimental observations. We must concentrate on the creation of ideal gRNA and the choice of suitable Cas enzymes in order to make genome editing with Clustered regularly interspaced short palindromic repeats far more accurate and feasible.

Probabilistic boolean networks predict transcription factor targets to induce transdifferentiation

We developed a computational approach to find the best intervention to achieve transcription factor (TF) mediated transdifferentiation. We construct probabilistic Boolean networks (PBNs) from single-cell RNA sequencing data of two different cell states to model hematopoietic transcription factors cross-talk. This was achieved by a “sampled network” approach, which enabled us to construct large networks. The interventions to induce transdifferentiation consisted of permanently activating or deactivating each of the TFs and determining the probability mass transfer of steady-state probabilities from the departure to the destination cell type or state. Our findings support the common assumption that TFs that are differentially expressed between the two cell types are the best intervention points to achieve transdifferentiation. TFs whose interventions are found to transdifferentiate progenitor B cells into monocytes include EBF1 down-regulation, CEBPB up-regulation, TCF3 down-regulation, and STAT3 up-regulation.

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Differentially expressed transcription factors are the best for transdifferentiation

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Probabilistic Boolean networks (PBNs) are used to model transdifferentiation using the scRNAseq data at one time point

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A new approach works for a large number of network nodes

New Hope for Genome Editing in Cultivated Grasses: CRISPR Variants and Application

With the advent of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated protein (Cas) mediated genome editing, crop improvement has progressed significantly in recent years. In this genome editing tool, CRISPR-associated Cas nucleases are restricted to their target of DNA by their preferred protospacer adjacent motifs (PAMs). A number of CRISPR-Cas variants have been developed e.g. CRISPR-Cas9, -Cas12a and -Cas12b, with different PAM requirements. In this mini-review, we briefly explain the components of the CRISPR-based genome editing tool for crop improvement. Moreover, we intend to highlight the information on the latest development and breakthrough in CRISPR technology, with a focus on a comparison of major variants (CRISPR-Cas9, -Cas12a, and -Cas12b) to the newly developed CRISPR-SpRY that have nearly PAM-less genome editing ability. Additionally, we briefly explain the application of CRISPR technology in the improvement of cultivated grasses with regard to biotic and abiotic stress tolerance as well as improving the quality and yield.

CRISPR/Cas9 System: A Potential Tool for Genetic Improvement in Floricultural Crops

Demand of flowers is increasing with time worldwide. Floriculture has become one of the most important commercial trades in agriculture. Although traditional breeding methods like hybridization and mutation breeding have contributed significantly to the development of important flower varieties, flower production and quality of flowers can be significantly improved by employing modern breeding approaches. Novel traits of significance have interest to consumers and producers, such as fragrance, new floral color, change in floral architecture and morphology, vase life, aroma, and resistance to biotic and abiotic stresses, have been introduced by genetic manipulation. The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system has recently emerged as a powerful genome-editing tool for accurately changing DNA sequences at specific locations. It provides excellent means of genetically improving floricultural crops. CRISPR/Cas system has been utilized in gene editing in horticultural cops. There are few reports on the utilization of the CRISPR/Cas9 system in flowers. The current review summarizes the research work done by employing the CRISPR/Cas9 system in floricultural crops including improvement in flowering traits such as color modification, prolonging the shelf life of flowers, flower initiation, and development, changes in color of ornamental foliage by genome editing. CRISPR/Cas9 gene editing could be useful in developing novel cultivars with higher fragrance and enhanced essential oil and many other useful traits. The present review also highlights the basic mechanism and key components involved in the CRISPR/Cas9 system.

CRISPR/Cas9 is a powerful tool for precise genome editing of legume crops: a review

Legumes are an imperative source of food and proteins across the globe. They also improve soil fertility through symbiotic nitrogen fixation (SNF). Genome editing (GE) is now a novel way of developing desirable traits in legume crops. Genome editing tools like clustered regularly interspaced short palindromic repeats (CRISPR) system permits a defined genome alteration to improve crop performance. This genome editing tool is reliable, cost-effective, and versatile, and it has to deepen in terms of use compared to other tools. Recently, many novel variations have drawn the attention of plant geneticists, and efforts are being made to develop trans-gene-free cultivars for ensuring biosafety measures. This review critically elaborates on the recent development in genome editing of major legumes crops. We hope this updated review will provide essential informations for the researchers working on legumes genome editing. In general, the CRISPR/Cas9 novel GE technique can be integrated with other techniques like omics approaches and next-generation tools to broaden the range of gene editing and develop any desired legumes traits. Regulatory ethics of CRISPR/Cas9 are also discussed.

CRISPR/Cas-based Diagnostics and Gene Therapy

Abstract Clustered regularly interspaced short palindromic repeats (CRISPR) technology, an easy, rapid, cost-effective, and precise gene-editing technique, has revolutionized diagnostics and gene therapy. Fast and accurate diagnosis of diseases is essential for point-of-care-testing (POCT) and specialized medical institutes. The CRISPR-associated (Cas) proteins system shed light on the new diagnostics methods at point-of-care (POC) owning to its advantages. In addition, CRISPR/Cas-based gene-editing technology has led to various breakthroughs in gene therapy. It has been employed in clinical trials for a variety of untreatable diseases, including cancer, blood disorders, and other syndromes. Currently, the clinical application of CRISPR/Cas has been mainly focused on ex vivo therapies. Recently, tremendous efforts have been made in the development of ex vivo gene therapy based on CRISPR-Cas9. Despite these efforts, in vivo CRISPR/Cas gene therapy is only in its initial stage. Here, we review the milestones of CRISPR/Cas technologies that advanced the field of diagnostics and gene therapy. We also highlight the recent advances of diagnostics and gene therapy based on CRISPR/Cas technology. In the last section, we discuss the strength and significant challenges of the CRISPR/Cas technology for its future clinical usage in diagnosis and gene therapy.

Employing CRISPR/Cas Technology for the Improvement of Potato and Other Tuber Crops

New breeding technologies have not only revolutionized biological science, but have also been employed to generate transgene-free products. Genome editing is a powerful technology that has been used to modify genomes of several important crops. This review describes the basic mechanisms, advantages and disadvantages of genome editing systems, such as ZFNs, TALENs, and CRISPR/Cas. Secondly, we summarize in detail all studies of the CRISPR/Cas system applied to potato and other tuber crops, such as sweet potato, cassava, yam, and carrot. Genes associated with self-incompatibility, abiotic-biotic resistance, nutrient-antinutrient content, and post-harvest factors targeted utilizing the CRISPR/Cas system are analyzed in this review. We hope that this review provides fundamental information that will be useful for future breeding of tuber crops to develop novel cultivars.

Clair G, Jones S, Svitashev S. Advances in Agrobacterium transformation and vector design result in high-frequency targeted gene insertion in maize

CRISPR-Cas is a powerful DNA double-strand break technology with wide-ranging applications in plant genome modification. However, the efficiency of genome editing depends on various factors including plant genetic transformation processes and types of modifications desired. Agrobacterium infection is the preferred method of transformation and delivery of editing components into the plant cell. While this method has been successfully used to generate gene knockouts in multiple crops, precise nucleotide replacement and especially gene insertion into a pre-defined genomic location remain highly challenging. Here, we report an efficient, selectable marker-free site-specific gene insertion in maize using Agrobacterium infection. Advancements in maize transformation and new vector design enabled increase of targeted insertion frequencies by two orders of magnitude in comparison to conventional Agrobacterium-mediated delivery. Importantly, these advancements allowed not only a significant improvement of the frequency, but also of the quality of generated events. These results further enable the application of genome editing for trait product development in a wide variety of crop species amenable to Agrobacterium-mediated transformation.

Loss of MAR1 Function is a Marker for Co-Selection of CRISPR-Induced Mutations in Plants

In this study, we describe the establishment of the knockout marker gene MAR1 for selection of CRISPR/Cas9-edited Arabidopsis seedlings and tomato explants in tissue culture. MAR1 encodes a transporter that is located in mitochondria and chloroplasts and is involved in iron homeostasis. It also opportunistically transports aminoglycoside antibiotics into these organelles and defects of the gene render plants insensitive to those compounds. Here, we show that mutations of MAR1 induced by the CRISPR system confer kanamycin-resistance to Arabidopsis plants and tomato tissues. MAR1 is single-copy in a variety of plant species and the corresponding proteins form a distinct phylogenetic clade allowing easy identification of MAR1 orthologs in different plants. We demonstrate that in multiplexing approaches, where Arabidopsis seedlings were selected via a CRISPR/Cas9-induced kanamycin resistance mediated by MAR1 mutation, a mutation in a second target gene was observed with higher frequency than in a control population only selected for the presence of the transgene. This so called co-selection has not been shown before to occur in plants. The technique can be employed to select for edited plants, which might be particularly useful if editing events are rare.

CRISPR-Based Genome Editing Tools: Insights into Technological Breakthroughs and Future Challenges

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.

Applicability of the EFSA Opinion on site-directed nucleases type 3 for the safety assessment of plants developed using site-directed nucleases type 1 and 2 and oligonucleotide-directed mutagenesis

The European Commission requested the EFSA Panel on Genetically Modified Organisms (GMO) to assess whether section 4 (hazard identification) and the conclusions of EFSA's Scientific opinion on the risk assessment of plants developed using zinc finger nuclease type 3 technique (ZFN-3) and other site-directed nucleases (SDN) with similar function are valid for plants developed via SDN-1, SDN-2 and oligonucleotide-directed mutagenesis (ODM). In delivering this Opinion, the GMO Panel compared the hazards associated with plants produced via SDN-1, SDN-2 and ODM with those associated with plants obtained via both SDN-3 and conventional breeding. Unlike for SDN-3 methods, the application of SDN-1, SDN-2 and ODM approaches aims to modify genomic sequences in a way which can result in plants not containing any transgene, intragene or cisgene. Consequently, the GMO Panel concludes that those considerations which are specifically related to the presence of a transgene, intragene or cisgene included in section 4 and the conclusions of the Opinion on SDN-3 are not relevant to plants obtained via SDN-1, SDN-2 or ODM as defined in this Opinion. Overall, the GMO Panel did not identify new hazards specifically linked to the genomic modification produced via SDN-1, SDN-2 or ODM as compared with both SDN-3 and conventional breeding. Furthermore, the GMO Panel considers that the existing Guidance for risk assessment of food and feed from genetically modified plants and the Guidance on the environmental risk assessment of genetically modified plants are sufficient but are only partially applicable to plants generated via SDN-1, SDN-2 or ODM. Indeed, those guidance documents' requirements that are linked to the presence of exogenous DNA are not relevant for the risk assessment of plants developed via SDN-1, SDN-2 or ODM approaches if the genome of the final product does not contain exogenous DNA.

Lentiviral Vector Pseudotypes: Precious Tools to Improve Gene Modification of Hematopoietic Cells for Research and Gene Therapy

Viruses have been repurposed into tools for gene delivery by transforming them into viral vectors. The most frequently used vectors are lentiviral vectors (LVs), derived from the human immune deficiency virus allowing efficient gene transfer in mammalian cells. They represent one of the safest and most efficient treatments for monogenic diseases affecting the hematopoietic system. LVs are modified with different viral envelopes (pseudotyping) to alter and improve their tropism for different primary cell types. The vesicular stomatitis virus glycoprotein (VSV-G) is commonly used for pseudotyping as it enhances gene transfer into multiple hematopoietic cell types. However, VSV-G pseudotyped LVs are not able to confer efficient transduction in quiescent blood cells, such as hematopoietic stem cells (HSC), B and T cells. To solve this problem, VSV-G can be exchanged for other heterologous viral envelopes glycoproteins, such as those from the Measles virus, Baboon endogenous retrovirus, Cocal virus, Nipah virus or Sendai virus. Here, we provide an overview of how these LV pseudotypes improved transduction efficiency of HSC, B, T and natural killer (NK) cells, underlined by multiple in vitro and in vivo studies demonstrating how pseudotyped LVs deliver therapeutic genes or gene editing tools to treat different genetic diseases and efficiently generate CAR T cells for cancer treatment.