Development of a reverse transcription droplet digital PCR assay for sensitive detection of peach latent mosaic viroid

CRISPR-Cas assisted diagnostics of plant viruses and challenges

Plant viruses threaten global food security by infecting commercial crops, highlighting the critical need for efficient virus detection to enable timely preventive measures. Current techniques rely on polymerase chain reaction (PCR) for viral genome amplification and require laboratory conditions. This review explores the applications of CRISPR-Cas assisted diagnostic tools, specifically CRISPR-Cas12a and CRISPR-Cas13a/d systems for plant virus detection and analysis. The CRISPR-Cas12a system can detect viral DNA/RNA amplicons and can be coupled with PCR or isothermal amplification, allowing multiplexed detection in plants with mixed infections. Recent studies have eliminated the need for expensive RNA purification, streamlining the process by providing a visible readout through lateral flow strips. The CRISPR-Cas13a/d system can directly detect viral RNA with minimal preamplification, offering a proportional readout to the viral load. These approaches enable rapid viral diagnostics within 30 min of leaf harvest, making them valuable for onsite field applications. Timely identification of diseases associated with pathogens is crucial for effective treatment; yet developing rapid, specific, sensitive, and cost-effective diagnostic technologies remains challenging. The current gold standard, PCR technology, has drawbacks such as lengthy operational cycles, high costs, and demanding requirements. Here we update the technical advancements of CRISPR-Cas in viral detection, providing insights into future developments, versatile applications, and potential clinical translation. There is a need for approaches enabling field plant viral nucleic acid detection with high sensitivity, specificity, affordability, and portability. Despite challenges, CRISPR-Cas-mediated pathogen diagnostic solutions hold robust capabilities, paving the way for ideal diagnostic tools. Alternative applications in virus research are also explored, acknowledging the technology's limitations and challenges.

Droplet digital PCR: A comprehensive tool for genetic analysis and prediction of bispecific antibody assembly during cell line development

Molecular biological methods have emerged as inevitable tools to accompany the process of cell line development for the generation of stable and highly productive manufacturing cell lines in the biopharmaceutical industry. PCR-based methods are especially useful for screening and characterization of cell lines due to their low cost, scalability, precision and propensity for multidimensional read-outs. In this study, the diverse applications of droplet digital PCR (ddPCR) as a molecular biological tool for cell line development are demonstrated. Specifically, it is shown that ddPCR can be used to enable precise, sensitive and reproducible absolute quantification of genomically integrated transgene copies during cell line development and cell bank characterization. Additionally, an amplitude multiplexing approach is applied to simultaneously run multiple assays on different genetic targets in a single reaction and advance clonal screening by measuring gene expression profiles to predict the assembly and homogeneity of difficult-to-express (DTE) proteins. The implementation of ddPCR-based assays during cell line development allows for early screening at a transcriptional level, particularly for complex, multidomain proteins, where balanced polypeptide chain ratios are of primary importance. Moreover, it is demonstrated that ddPCR-based genomic characterization improves the robustness, efficiency and comparability of absolute transgene copy number quantification, an essential genetic parameter that must be demonstrated to regulatory authorities during clinical trial and market authorization application submissions to support genetic stability and consistency of the selected cell substrate.

Current and emerging trends in techniques for plant pathogen detection

Plant pathogenic microorganisms cause substantial yield losses in several economically important crops, resulting in economic and social adversity. The spread of such plant pathogens and the emergence of new diseases is facilitated by human practices such as monoculture farming and global trade. Therefore, the early detection and identification of pathogens is of utmost importance to reduce the associated agricultural losses. In this review, techniques that are currently available to detect plant pathogens are discussed, including culture-based, PCR-based, sequencing-based, and immunology-based techniques. Their working principles are explained, followed by an overview of the main advantages and disadvantages, and examples of their use in plant pathogen detection. In addition to the more conventional and commonly used techniques, we also point to some recent evolutions in the field of plant pathogen detection. The potential use of point-of-care devices, including biosensors, have gained in popularity. These devices can provide fast analysis, are easy to use, and most importantly can be used for on-site diagnosis, allowing the farmers to take rapid disease management decisions.

Detection and Quantification of Apple Stem Grooving Virus in Micropropagated Apple Plantlets Using Reverse-Transcription Droplet Digital PCR

Apple stem grooving virus (ASGV) is a destructive viral pathogen of pome fruit trees that causes significant losses to fruit production worldwide. Obtaining ASGV-free propagation materials is essential to reduce economic losses, and accurate and sensitive detection methods to screen ASGV-free plantlets during in vitro propagation are urgently necessary. In this study, ASGV was sensitively and accurately quantified from in vitro propagated apple plantlets using a reverse transcription droplet digital polymerase chain reaction (RT-ddPCR) assay. The optimized RT-ddPCR assay was specific to other apple viruses, and was at least 10-times more sensitive than RT-real-time quantitative PCR assay. Furthermore, the optimized RT-ddPCR assay was validated for the detection and quantification of ASGV using micropropagated apple plantlet samples. This RT-ddPCR assay can be utilized for the accurate quantitative detection of ASGV infection in ASGV-free certification programs, and can thus contribute to the production of ASGV-free apple trees.

Reliable and rapid identification of glyphosate-resistance in the invasive weed Amaranthus palmeri in China

BACKGROUND

Glyphosate-resistant invasive plants, including Amaranthus palmeri S. Watson, have greatly challenged management of new invasions. Elucidating their glyphosate resistance levels rapidly and accurately will better inform management strategies. Quantitative real-time PCR (qPCR) has been used to identify glyphosate resistance in A. palmeri by detecting gene copy numbers of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), an enzyme inhibited by glyphosate. However, qPCR can only indirectly determine copy numbers because it requires a calibrator sample; it also lacks standardization, thus limiting its usefulness. Droplet digital PCR (ddPCR) is a new method to detect copy number directly and precisely. We evaluated ddPCR as a tool to determine glyphosate-resistance level while using qPCR and glyphosate dose response (GDR) assays as reference technologies to compare performance and efficiency between methods.

RESULTS

We identified seven susceptible and seven resistant populations of A. palmeri using the GDR assay. Resistant levels detected by qPCR and ddPCR were generally consistent with the GDR results. Although detected values obtained by qPCR and ddPCR were highly correlated (R2  = 0.94), ddPCR results had a lower proportion of non-ideal values (36%) with better accuracy (100%) and specificity (100%) than those of qPCR results.

CONCLUSIONS

Our findings demonstrate that ddPCR offers improved accuracy and specificity in detecting EPSPS gene copy numbers and is a robust and rapid method for glyphosate-resistance identification in A. palmeri. Our research is the first to measure glyphosate resistance in A. palmeri by ddPCR assay and will shed light on future applications of ddPCR in identifying herbicide resistance in other invasive weeds. © 2022 Society of Chemical Industry.

Development and application of reverse transcription droplet digital PCR assay for sensitive detection of apple scar skin viroid during in vitro propagation of apple plantlets

Apple scar skin viroid (ASSVd), of the genus Apscaviroid, causes serious pome fruit diseases, such as apple scar skin, dapple apple, pear rusty skin, pear fruit crinkle, and pear dimple fruit. This study aimed at establishing a sensitive and accurate method for quantification of ASSVd in apple leaves and plantlets using a reverse transcription droplet digital polymerase chain reaction (RT-ddPCR) assay. The specificity was analyzed using other apple viruses, and the negative amplification of the cross-reaction assay demonstrated the high specificity of RT-ddPCR. The detection limit of ASSVd by RT-ddPCR was 1.75 × 10² copies/μL (0.14 concentration), and the sensitivity was ten-fold higher than that of RT-qPCR. Similarly, positive detection in apple plantlet samples by RT-ddPCR was higher than that by RT-qPCR. The RT-ddPCR assay represents a promising alternative for accurate quantitative detection and diagnosis of ASSVd infection in ASSVd-free certification programs.