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Systematic synthesis of CRISPR/Cas applications for enhancing salt tolerance in crops: a decade of progress and challenges.
Soil salinity is a major constraint on global crop productivity, driving the need for salt-tolerant varieties. While CRISPR-Cas genome editing offers targeted solutions for trait improvement, significant biological and technical bottlenecks limit its application in conferring salt stress resilience. This systematic summarizes findings from 83 peer-reviewed studies (2015-2024) employing CRISPR/Cas technologies to improve salt tolerance in five major crops (rice, wheat, maize, sorghum, barley). Our systematic review reveals that early single-gene edits achieved modest gains (30-50% Na⁺ exclusion) but often showed limited yield gains in field settings, potentially due to compensatory regulation and environmental variation. The literature suggests that multiplex designs spanning ion homeostasis, osmoprotection, and ROS management can improve salt-tolerance outcomes and help maintain yield under severe salinity; however, the magnitude of benefit varies with crop, genotype, and transformation/regeneration context. Protein-protein interaction networks identified 12 hub genes and three functional modules, highlighting SOS3 and MPK6 as critical bottlenecks whose disruption risks pleiotropic effects. Spatial expression analysis underscored tissue-specific trade-offs, constitutive editing of root-dominant genes in shoots reduced yields by 15-28%, while tissue-optimized promoters minimized physiological conflicts. Persistent challenges include genotype-dependent transformation inefficiencies, epigenetic drift and environmental interactions under salt stress. Collectively, our synthesis consolidates and refines current best practices for salt-tolerance genome editing and highlights major bottlenecks-particularly regeneration/transformability, genotype dependence, and epigenetic constraints-that should be explicitly considered in experimental design and reporting.
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Split-marker-mediated genome editing improves homologous recombination frequency in the CTG clade yeast Candida intermedia.
Genome-editing toolboxes are essential for the exploration and exploitation of nonconventional yeast species as cell factories, as they facilitate both genome studies and metabolic engineering. The nonconventional yeast Candida intermedia is a biotechnologically interesting species due to its capacity to convert a wide range of carbon sources, including xylose and lactose found in forestry and dairy industry waste and side-streams, into added-value products. However, possibilities of genetic manipulation have so far been limited due to lack of molecular tools for this species. We describe here the development of a genome editing method for C. intermedia, based on electroporation and gene deletion cassettes containing the Candida albicans NAT1 dominant selection marker flanked by 1000 base pair sequences homologous to the target loci. Linear deletion cassettes targeting the ADE2 gene originally resulted in <1% targeting efficiencies, suggesting that C. intermedia mainly uses nonhomologous end joining for integration of foreign DNA fragments. By developing a split-marker based deletion technique for C. intermedia, we successfully improved the homologous recombination rates, achieving targeting efficiencies up to 70%. For marker-less deletions, we also employed the split-marker cassette in combination with a recombinase system, which enabled the construction of double deletion mutants via marker recycling. Overall, the split-marker technique proved to be a quick and reliable method for generating gene deletions in C. intermedia, which opens the possibility to uncover and enhance its cell factory potential.
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The Codon Usage Bias Analysis of Free-Living Ciliates' Macronuclear Genomes and Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 Vector Construction of Stylonychia lemnae.
Ciliates represent higher unicellular animals, and several species are also important model organisms for molecular biology research. Analyses of codon usage bias (CUB) of the macronuclear (MAC) genome in ciliates can not only promote a better understanding of the genetic mode and evolution history of these organisms but also help optimize codons to improve the gene editing efficiency of model ciliates. In this study, macronuclear genome sequences of nine free-living ciliates were analyzed with CodonW software to calculate the following indices: the guanine-cytosine content (GC); the frequency of the nucleotides U, C, A, and G at the third position of codons (U3s, C3s, A3s, G3s); the effective number of codons (ENC); the correlation between GC at the first and second positions (GC12); the frequency of the nucleotides G + C at the third position of synonymous codons (GC3s); the relative synonymous codon usage (RSCU). Parity rule 2 plot analysis, neutrality plot analysis, and correlation analysis were performed to explore the factors that influence codon preference. The results showed that the GC contents in nine ciliates' MAC genomes were lower than 50% and appeared AT-rich. The base compositions of GC12 and GC3s are markedly distinct and the codon usage pattern and evolution of ciliates are affected by genetic mutation and natural selection. According to the synonymous codon analysis, the codons of most ciliates ended with A or U and eight codons were the general optimal codons of nine ciliates. A clustered regularly interspaced short palindromic repeats/Cas9 (CRISPR/Cas9) expression vector of Stylonychia lemnae was constructed by optimizing the macronuclear genome codon and was successfully used to knock out the Adss gene. This is the first such extensive investigation of the MAC genome CUB of ciliates and the initial successful application of the CRISPR/Cas9 technique in free-living ciliates.
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One-Step Biological Upcycling of Chitin Wastes into Violacein by Engineered Chromobacterium violaceum.
Existing technologies for the valorization of organic wastes have been focused mainly on degradable wastes, while an efficient, low-carbon approach for the upcycling of shell waste is still lacking. Here, we report a one-step chitin biological fermentation process (CBFP), based on the construction of Chromobacterium violaceum engineered strain, for efficiently converting shell waste-derived chitin into high-value violacein. A high-efficiency CRISPR cytosine-base editor (pRK2-BE, 97% editing efficiency) was developed for C. violaceum, which demonstrated cv_4240, cv_1440, and cv_2935 as the major chitin hydrolysis genes and phosphoenolpyruvate-carbohydrate phosphotransferase system (PTS) as the major N-acetyl-glucosamine uptake pathway. The engineered strain WT/pBAD-4, co-overexpressing of cv_4240, cv_1440, cv_2935, and vioABCDE, efficiently utilized colloidal chitin and crystalline chitin as the sole carbon and nitrogen source, achieving violacein yields of 159.78 and 120.95 mg·L-1, respectively. This study provided an economically viable and environmentally sustainable solution for green upcycling of shell waste.
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Gene Repression in Haloarchaea Using the CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas I-B System.
The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system is used by bacteria and archaea to fend off foreign genetic elements. Since its discovery it has been developed into numerous applications like genome editing and regulation of transcription in eukaryotes and bacteria. For archaea currently no tools for transcriptional repression exist. Because molecular biology analyses in archaea become more and more widespread such a tool is vital for investigating the biological function of essential genes in archaea. Here we use the model archaeon Haloferax volcanii to demonstrate that its endogenous CRISPR-Cas system I-B can be harnessed to repress gene expression in archaea. Deletion of cas3 and cas6b genes results in efficient repression of transcription. crRNAs targeting the promoter region reduced transcript levels down to 8%. crRNAs targeting the reading frame have only slight impact on transcription. crRNAs that target the coding strand repress expression only down to 88%, whereas crRNAs targeting the template strand repress expression down to 8%. Repression of an essential gene results in reduction of transcription levels down to 22%. Targeting efficiencies can be enhanced by expressing a catalytically inactive Cas3 mutant. Genes can be targeted on plasmids or on the chromosome, they can be monocistronic or part of a polycistronic operon.
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Are the current gRNA ranking prediction algorithms useful for genome editing in plants?
Introducing a new trait into a crop through conventional breeding commonly takes decades, but recently developed genome sequence modification technology has the potential to accelerate this process. One of these new breeding technologies relies on an RNA-directed DNA nuclease (CRISPR/Cas9) to cut the genomic DNA, in vivo, to facilitate the deletion or insertion of sequences. This sequence specific targeting is determined by guide RNAs (gRNAs). However, choosing an optimum gRNA sequence has its challenges. Almost all current gRNA design tools for use in plants are based on data from experiments in animals, although many allow the use of plant genomes to identify potential off-target sites. Here, we examine the predictive uniformity and performance of eight different online gRNA-site tools. Unfortunately, there was little consensus among the rankings by the different algorithms, nor a statistically significant correlation between rankings and in vivo effectiveness. This suggests that important factors affecting gRNA performance and/or target site accessibility, in plants, are yet to be elucidated and incorporated into gRNA-site prediction tools.
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CRISPR-assisted rational flux-tuning and arrayed CRISPRi screening of an L-proline exporter for L-proline hyperproduction.
Development of hyperproducing strains is important for biomanufacturing of biochemicals and biofuels but requires extensive efforts to engineer cellular metabolism and discover functional components. Herein, we optimize and use the CRISPR-assisted editing and CRISPRi screening methods to convert a wild-type Corynebacterium glutamicum to a hyperproducer of L-proline, an amino acid with medicine, feed, and food applications. To facilitate L-proline production, feedback-deregulated variants of key biosynthetic enzyme γ-glutamyl kinase are screened using CRISPR-assisted single-stranded DNA recombineering. To increase the carbon flux towards L-proline biosynthesis, flux-control genes predicted by in silico analysis are fine-tuned using tailored promoter libraries. Finally, an arrayed CRISPRi library targeting all 397 transporters is constructed to discover an L-proline exporter Cgl2622. The final plasmid-, antibiotic-, and inducer-free strain produces L-proline at the level of 142.4 g/L, 2.90 g/L/h, and 0.31 g/g. The CRISPR-assisted strain development strategy can be used for engineering industrial-strength strains for efficient biomanufacturing.
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CRISPR-based one-pot detection: A game-changer in nucleic acid analysis.
The CRISPR/Cas system, originally developed as a gene-editing tool, has rapidly emerged as a powerful platform for nucleic acid detection due to its remarkable specificity, programmability, and robust trans-cleavage activity. While conventional CRISPR-based assays typically require separate amplification and detection steps, introducing complexity, manual intervention, and contamination risks. Recent innovations have led to the development of one-pot detection strategies that integrate target amplification with Cas-mediated signal generation within a single reaction vessel. These streamlined systems not only reduce handling steps and turnaround time but also enhance sensitivity and enable multiplexed detection of low-abundance nucleic acid targets. As such, one-pot CRISPR diagnostics are poised to transform point-of-care testing, pathogen surveillance, and clinical diagnostics. In this review, we summarize the latest advances in one-pot CRISPR-based detection technologies, evaluate their current limitations, and discuss strategies for optimization. Future efforts should focus on refining reaction kinetics, improving reagent stability, reducing costs, and expanding the repertoire of detectable targets. Furthermore, integration with portable platforms, AI-assisted signal interpretation, and the discovery of novel Cas effectors will be pivotal in realizing the full potential of CRISPR-based one-pot systems in diverse real-world applications.
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Highly efficient correction of structural mutations of 450 kb KIT locus in kidney cells of Yorkshire pig by CRISPR/Cas9.
The white coat colour of Yorkshire and Landrace pig breeds is caused by the dominant white I allele of KIT, associated with 450-kb duplications and a splice mutation (G > A) at the first base in intron 17. To test whether genome editing can be employed to correct this structural mutation, and to investigate the role of KIT in the control of porcine coat colour, we designed sgRNAs targeting either intron 16 or intron 17 of KIT, and transfected Cas9/sgRNA co-expression plasmids into the kidney cells of Yorkshire pigs. The copy number of KIT was reduced by about 13%, suggesting the possibility of obtaining cells with corrected structural mutations of the KIT locus. Using single cell cloning, from 24 successfully expanded single cell clones derived from cells transfected with sgRNA targeting at intron 17, we obtained 3 clones with a single copy of KIT without the splice mutation. Taken together, the 12.5% (3/24) efficiency of correction of structural mutations of 450 kb fragments is highly efficient, providing a solid basis for the generation of genome edited Yorkshire pigs with a normal KIT locus. This provides an insight into the underlying genetic mechanisms of porcine coat colour.
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Cleavage of DNA Substrate Containing Nucleotide Mismatch in the Complementary Region to sgRNA by Cas9 Endonuclease: Thermodynamic and Structural Features.
The non-ideal accuracy and insufficient selectivity of CRISPR/Cas9 systems is a serious problem for their use as a genome editing tool. It is important to select the target sequence correctly so that the CRISPR/Cas9 system does not cut similar sequences. This requires an understanding of how and why mismatches in the target sequence can affect the efficiency of the Cas9/sgRNA complex. In this work, we studied the catalytic activity of the Cas9 enzyme to cleave DNA substrates containing nucleotide mismatch at different positions relative to the PAM in the "seed" sequence. We show that mismatches in the complementarity of the sgRNA/DNA duplex at different positions relative to the protospacer adjacent motif (PAM) sequence tend to decrease the cleavage efficiency and increase the half-maximal reaction time. However, for two mismatches at positions 11 and 20 relative to the PAM, an increase in cleavage efficiency was observed, both with and without an increase in half-reaction time. Thermodynamic parameters were obtained from molecular dynamics results, which showed that mismatches at positions 8, 11, and 20 relative to the PAM thermodynamically stabilize the formed complex, and a mismatch at position 2 of the PAM fragment exerts the greatest stabilization compared to the original DNA sequence. The weak correlation of the thermodynamic binding parameters of the components of the Cas9/sgRNA:dsDNA complex with the cleavage data of DNA substrates containing mismatches indicates that the efficiency of Cas9 operation is mainly affected by the conformational changes in Cas9 and the mutual arrangement of sgRNA and substrates.
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