Efficiency, Specificity and Temperature Sensitivity of Cas9 and Cas12a RNPs for DNA-free Genome Editing in Plants

CRISPR/Cas system: A revolutionary tool for crop improvement

World's population is elevating at an alarming rate thus, the rising demands of producing crops with better adaptability to biotic and abiotic stresses, superior nutritional as well as morphological qualities, and generation of high-yielding varieties have led to encourage the development of new plant breeding technologies. The availability and easy accessibility of genome sequences for a number of crop plants as well as the development of various genome editing technologies such as zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) has opened up possibilities to develop new varieties of crop plants with superior desirable traits. However, these approaches has limitation of being more expensive as well as having complex steps and time-consuming. The CRISPR/Cas genome editing system has been intensively studied for allowing versatile target-specific modifications of crop genome that fruitfully aid in the generation of novel varieties. It is an advanced and promising technology with the potential to meet hunger needs and contribute to food production for the ever-growing human population. This review summarizes the usage of novel CRISPR/Cas genome editing tool for targeted crop improvement in stress resistance, yield, quality and nutritional traits in the desired crop plants.

The Cutting-edge of CRISPR for Cancer Treatment and its Future Prospects

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a versatile technology that allows precise modification of genes. One of its most promising applications is in cancer treatment. By targeting and editing specific genes involved in cancer development and progression, CRISPR has the potential to become a powerful tool in the fight against cancer. This review aims to assess the recent progress in CRISPR technology for cancer research and to examine the obstacles and potential strategies to address them. The two most commonly used CRISPR systems for gene editing are CRISPR/Cas9 and CRISPR/Cas12a. CRISPR/Cas9 employs different repairing systems, including homologous recombination (HR) and nonhomologous end joining (NHEJ), to introduce precise modifications to the target genes. However, off-target effects and low editing efficiency are some of the main challenges associated with this technology. To overcome these issues, researchers are exploring new delivery methods and developing CRISPR/Cas systems with improved specificity. Moreover, there are ethical concerns surrounding using CRISPR in gene editing, including the potential for unintended consequences and the creation of genetically modified organisms. It is important to address these issues through rigorous testing and strict regulations. Despite these challenges, the potential benefits of CRISPR in cancer therapy cannot be overlooked. By introducing precise modifications to cancer cells, CRISPR could offer a targeted and effective treatment option for patients with different types of cancer. Further investigation and development of CRISPR technology are necessary to overcome the existing challenges and harness its full potential in cancer therapy.

A Variant of LbCas12a and Elevated Incubation Temperatures Enhance the Rate of Gene Editing in the Oomycete Phytophthora infestans

CRISPR-Cas editing systems have proved to be powerful tools for functional genomics research, but their effectiveness in many non-model species remains limited. In the potato and tomato pathogen Phytophthora infestans, an editing system was previously developed that expresses the Lachnospiracae bacterium Cas12a endonuclease (LbCas12a) and guide RNA from a DNA vector. However, the method works at low efficiency. Based on a hypothesis that editing is constrained by a mismatch between the optimal temperatures for P. infestans growth and endonuclease catalysis, we tested two strategies that increased the frequency of editing of two target genes by about 10-fold. First, we found that editing was boosted by a mutation in LbCas12a (D156R) that had been reported to expand its catalytic activity over a broader temperature range. Second, we observed that editing was enhanced by transiently incubating transformed tissue at a higher temperature. These modifications should make CRISPR-Cas12a more useful for interrogating gene and protein function in P. infestans and its relatives, especially species that grow optimally at lower temperatures. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Generation of the transgene-free canker-resistant Citrus sinensis using Cas12a/crRNA ribonucleoprotein in the T0 generation

Citrus canker caused by Xanthomonas citri subsp. citri (Xcc) is a destructive citrus disease worldwide. Generating disease-resistant cultivars is the most effective, environmentally friendly and economic approach for disease control. However, citrus traditional breeding is lengthy and laborious. Here, we develop transgene-free canker-resistant Citrus sinensis lines in the T0 generation within 10 months through transformation of embryogenic protoplasts with Cas12a/crRNA ribonucleoprotein to edit the canker susceptibility gene CsLOB1. Among the 39 regenerated lines, 38 are biallelic/homozygous mutants, demonstrating a 97.4% biallelic/homozygous mutation rate. No off-target mutations are detected in the edited lines. Canker resistance of the cslob1-edited lines results from both abolishing canker symptoms and inhibiting Xcc growth. The transgene-free canker-resistant C. sinensis lines have received regulatory approval by USDA APHIS and are exempted from EPA regulation. This study provides a sustainable and efficient citrus canker control solution and presents an efficient transgene-free genome-editing strategy for citrus and other crops.

Editing efficiencies with Cas9 orthologs, Cas12a endonucleases, and temperature in rice

The advent of CRISPR-Cas technology has made it the genome editing tool of choice in all kingdoms of life, including plants, which can have large, highly duplicated genomes. As a result, finding adequate target sequences that meet the specificities of a given Cas nuclease on any gene of interest remains challenging in many cases. To assess target site flexibility, we tested five different Cas9/Cas12a endonucleases (SpCas9, SaCas9, St1Cas9, Mb3Cas12a, and AsCas12a) in embryogenic rice calli from Taipei 309 at 37°C (optimal temperature for most Cas9/Cas12a proteins) and 27°C (optimal temperature for tissue culture) and measured their editing rates under regular tissue culture conditions using Illumina sequencing. StCas9 and AsCas12 were not functional as tested, regardless of the temperature used. SpCas9 was the most efficient endonuclease at either temperature, regardless of whether monoallelic or biallelic edits were considered. Mb3Cas12a at 37°C was the next most efficient endonuclease. Monoallelic edits prevailed for both SaCas9 and Mb3Cas12a at 27°C, but biallelic edits prevailed at 37°C. Overall, the use of other Cas9 orthologs, the use of Cas12a endonucleases, and the optimal temperature can expand the range of targetable sequences.

A Robust Expression and Purification Method for Production of SpCas9-GFP-MBP Fusion Protein for In Vitro Applications

Genome editing using the CRISPR/Cas9 system is one of the trendiest methodologies in the scientific community. Many genome editing approaches require recombinant Streptococcus pyogenes Cas9 (SpCas9) at some point during their application, for instance, for in vitro validation of single guide RNAs (SgRNAs) or for the DNA-free editing of genes of interest. Hereby, we provide a simple and detailed expression and purification protocol for SpCas9 as a protein fused to GFP and MBP. This protocol improves protein yield and simplifies the purification process by overcoming the frequently occurring obstacles such as plasmid loss, inconsistent protein expression levels, or inadequate protein binding to affinity resins. On average, this protocol yields 10 to 30 mg of purified, active, His6−MBP−SpCas9 NLS−GFP protein. The purity addressed through SDS-PAGE is > 80%.

Tissue Culture and Somatic Embryogenesis in Warm-Season Grasses—Current Status and Its Applications: A Review

Warm-season grasses are C4 plants and have a high capacity for biomass productivity. These grasses are utilized in many agricultural production systems with their greatest value as feeds for livestock, bioethanol, and turf. However, many important warm-season perennial grasses multiply either by vegetative propagation or form their seeds by an asexual mode of reproduction called apomixis. Therefore, the improvement of these grasses by conventional breeding is difficult and is dependent on the availability of natural genetic variation and its manipulation through breeding and selection. Recent studies have indicated that plant tissue culture system through somatic embryogenesis complements and could further develop conventional breeding programs by micropropagation, somaclonal variation, somatic hybridization, genetic transformation, and genome editing. This review summarizes the tissue culture and somatic embryogenesis in warm-season grasses and focus on current status and above applications including the author’s progress.