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Background CRISPR-Cas systems endow bacterial and archaeal species with adaptive immunity mechanisms to fend off invading phages and foreign genetic elements. CRISPR-Cas9 has been harnessed to confer virus interference against DNA viruses in eukaryotes, including plants. In addition, CRISPR-Cas13 systems have been used to target RNA viruses and the transcriptome in mammalian and plant cells. Recently, CRISPR-Cas13a has been shown to confer modest interference against RNA viruses. Here, we characterized a set of different Cas13 variants to identify those with the most efficient, robust, and specific interference activities against RNA viruses in planta using Nicotiana benthamiana . Results Our data show that LwaCas13a, PspCas13b, and CasRx variants mediate high interference activities against RNA viruses in transient assays. Moreover, CasRx mediated robust interference in both transient and stable overexpression assays when compared to the other variants tested. CasRx targets either one virus alone or two RNA viruses simultaneously, with robust interference efficiencies. In addition, CasRx exhibits strong specificity against the target virus and does not exhibit collateral activity in planta . Conclusions Our data establish CasRx as the most robust Cas13 variant for RNA virus interference applications in planta and demonstrate its suitability for studying key questions relating to virus biology.

Summary Plant diseases caused by viruses limit crop production and quality, resulting in significant losses. However, options for managing viruses are limited; for example, as systemic obligate parasites, they cannot be killed by chemicals. Sensitive, robust, affordable diagnostic assays are needed to detect the presence of viruses in plant materials such as seeds, vegetative parts, insect vectors, or alternative hosts and then prevent or limit their introduction into the field by destroying infected plant materials or controlling insect hosts. Diagnostics based on biological and physical properties are not very sensitive and are time‐consuming, but assays based on viral proteins and nucleic acids are more specific, sensitive, and rapid. However, most such assays require laboratories with sophisticated equipment and technical skills. By contrast, isothermal‐based assays such as loop‐mediated isothermal amplification (LAMP) and recombinase polymerase amplification (RPA) are simple, easy to perform, reliable, specific, and rapid and do not require specialized equipment or skills. Isothermal amplification assays can be performed using lateral flow devices, making them suitable for onsite detection or testing in the field. To overcome non‐specific amplification and cross‐contamination issues, isothermal amplification assays can be coupled with CRISPR/Cas technology. Indeed, the collateral activity associated with some CRISPR/Cas systems has been successfully harnessed for visual detection of plant viruses. Here, we briefly describe traditional methods for detecting viruses and then examine the various isothermal assays that are being harnessed to detect viruses.

Background CRISPR/Cas systems confer immunity against invading nucleic acids and phages in bacteria and archaea. CRISPR/Cas13a (known previously as C2c2) is a class 2 type VI-A ribonuclease capable of targeting and cleaving single-stranded RNA (ssRNA) molecules of the phage genome. Here, we employ CRISPR/Cas13a to engineer interference with an RNA virus, Turnip Mosaic Virus (TuMV), in plants. Results CRISPR/Cas13a produces interference against green fluorescent protein (GFP)-expressing TuMV in transient assays and stable overexpression lines of Nicotiana benthamiana. CRISPR RNA (crRNAs) targeting the HC-Pro and GFP sequences exhibit better interference than those targeting other regions such as coat protein (CP) sequence. Cas13a can also process pre-crRNAs into functional crRNAs. Conclusions Our data indicate that CRISPR/Cas13a can be used for engineering interference against RNA viruses, providing a potential novel mechanism for RNA-guided immunity against RNA viruses and for other RNA manipulations in plants.

One important factor for successful disease management is the ability to rapidly and accurately identify the causal agent. Plant viruses cause severe economic losses and pose a serious threat to sustainable agriculture. Therefore, optimization of the speed, sensitivity, feasibility, portability, and accuracy of virus detection is urgently needed. Here, we developed a clustered regularly interspaced short palindromic repeats (CRISPR)-based nucleic acid diagnostic method utilizing the CRISPR–Cas12a system for detecting two geminiviruses, tomato yellow leaf curl virus (TYLCV) and tomato leaf curl New Delhi virus (ToLCNDV), which have single-stranded DNA genomes. Our assay detected TYLCV and ToLCNDV in infected plants with high sensitivity and specificity. Our newly developed assay can be performed in ~1 h and provides easy-to-interpret visual readouts using a simple, low-cost fluorescence visualizer, making it suitable for point-of-use applications.

In plants, homology‐directed repair is inefficient, limiting our ability to make precise edits of the DNA sequence (Ali et al., 2020; Butt et al., 2017). [...]cytosine and adenine base editors have serious drawbacks including lower efficiency, unclean edited sequence and the possibility of off‐target mutations at other loci (Rees and Liu, 2018). By these mutations, PvUII site was lost and two sites Pst1 and BbsI were generated. (f) The PvUII enriched DNA samples are confirmed by Sanger sequencing. (g) Schematic of rice locus TB1 (TEOSINTE BRANCHED1). The OsIPA transcription factor reduces the number of unproductive tillers and improves rice yield. [...]we targeted rice TEOSINTE BRANCHED 1 (OsTB1), a member of the TEOSINTE BRANCHED1, CYCLOIDEA AND PCF TRANSCRIPTION FACTOR gene family (Figure 1g).

Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) systems are key immune mechanisms helping prokaryotic species fend off RNA and DNA viruses. CRISPR/Cas9 has broad applications in basic research and biotechnology and has been widely used across eukaryotic species for genome engineering and functional analysis of genes. The recently developed CRISPR/Cas13 systems target RNA rather than DNA and thus offer new potential for transcriptome engineering and combatting RNA viruses. Here, we used CRISPR/LshCas13a to stably engineer Arabidopsis thaliana for interference against the RNA genome of Turnip mosaic virus (TuMV). Our data demonstrate that CRISPR RNAs (crRNAs) guiding Cas13a to the sequences encoding helper component proteinase silencing suppressor (HC-Pro) or GFP target 2 (GFP-T2) provide better interference compared to crRNAs targeting other regions of the TuMV RNA genome. This work demonstrates the exciting potential of CRISPR/Cas13 to be used as an antiviral strategy to obstruct RNA viruses, and encourages the search for more robust and effective Cas13 variants or CRISPR systems that can target RNA.

Genomic surveillance of SARS-CoV-2 is important for understanding both the evolution and the patterns of local and global transmission. Here, we generated 311 SARS-CoV-2 genomes from samples collected in coastal Kenya between 17 th March and 31 st July 2020. We estimated multiple independent SARS-CoV-2 introductions into the region were primarily of European origin, although introductions could have come through neighbouring countries. Lineage B.1 accounted for 74% of sequenced cases. Lineages A, B and B.4 were detected in screened individuals at the Kenya-Tanzania border or returning travellers. Though multiple lineages were introduced into coastal Kenya following the initial confirmed case, none showed extensive local expansion other than lineage B.1. International points of entry were important conduits of SARS-CoV-2 importations into coastal Kenya and early public health responses prevented established transmission of some lineages. Undetected introductions through points of entry including imports from elsewhere in the country gave rise to the local epidemic at the Kenyan coast. SARS-CoV-2 was first detected in Kenya in March 2020 and there was evidence of local transmission in the following months. Here, the authors characterise the early stages of the epidemic in coastal Kenya using phylogenetics and find evidence of multiple strain importations from international points of entry.

Background Artemisinin-based combination therapy (ACT) has been first-line treatment for uncomplicated malaria in sub-Saharan Africa for over two decades. However, emerging artemisinin partial resistance threatens efficacy. Multiple first-line treatments (MFTs) represent a proposed mitigation strategy, though associated health systems challenges remain unknown. This study evaluated health systems challenges and facilitators for MFT implementation in western Kenya. Methods A 2 year pilot study (June 2020–June 2022) implemented adaptive cycling of four artemisinin-based combinations: Artemether-Lumefantrine (AL), Dihydroartemisin-Piperaquine (DHA-PIP), Amodiaquine-Artesunate (ASAQ), and Pyronaridine-Artesunate (PYR-ART) in western Kenya. Homa Bay (implementation) and Migori (control) counties were compared. Implementation involved 8 month drug cycling on mainland and 12 month cycling on Mfangano Island, while control county continued AL throughout. Adult patients diagnosed with uncomplicated malaria were included (pregnant women and children < 5 years excluded). Health systems assessment used semi-structured questionnaires, key informant interviews, and exit interviews. Outcome measures included diagnostic kit availability, procurement logistics, information system alignment, human resources, stakeholder acceptance, and side effects. Costs were tracked using ingredient approach, and malaria cases compared between counties. Results MFT was accepted by key stakeholders. One minor adverse effect (vomiting) was reported. Patients preferred simple once-daily dosing of new drugs over AL's complicated regimen. Major challenges included logistics inefficiencies in drug quantification and stock management, human resource constraints, information system reconfiguration needs, and frequent diagnostic kit stock-outs. Start-up and implementation costs were roughly equal. Economic cost per patient treated was USD 3, lower than reported elsewhere in sub-Saharan Africa. Digital health tools (SMS/WhatsApp) facilitated implementation through improved communication and follow-up. Migori (control) showed 12.5 percentage points higher malaria positivity rates (23.3% vs 10.8%) with better directional consistency. Testing efficiency differed markedly (4.3 vs 9.2 tests per positive case) between counties. Conclusion Adaptive cycling MFT implementation is feasible in Kenya with adequate planning and addressing health systems challenges. Stakeholder engagement and continuous training were critical for success. Policy implications and regional cooperation potential warrant exploration in other sub-Saharan African countries with different deployment contexts.

The high proportion of SARS-CoV-2 infections that have remained undetected presents a challenge to tracking the progress of the pandemic and estimating the extent of population immunity. We used residual blood samples from women attending antenatal care services at three hospitals in Kenya between August 2020 and October 2021and a validated IgG ELISA for SARS-Cov-2 spike protein and adjusted the results for assay sensitivity and specificity. We fitted a two-component mixture model as an alternative to the threshold analysis to estimate of the proportion of individuals with past SARS-CoV-2 infection. We estimated seroprevalence in 2,981 women; 706 in Nairobi, 567 in Busia and 1,708 in Kilifi. By October 2021, 13% of participants were vaccinated (at least one dose) in Nairobi, 2% in Busia. Adjusted seroprevalence rose in all sites; from 50% (95%CI 42-58) in August 2020, to 85% (95%CI 78-92) in October 2021 in Nairobi; from 31% (95%CI 25-37) in May 2021 to 71% (95%CI 64-77) in October 2021 in Busia; and from 1% (95% CI 0-3) in September 2020 to 63% (95% CI 56-69) in October 2021 in Kilifi. Mixture modelling, suggests adjusted cross-sectional prevalence estimates are underestimates; seroprevalence in October 2021 could be 74% in Busia and 72% in Kilifi. There has been substantial, unobserved transmission of SARS-CoV-2 in Nairobi, Busia and Kilifi Counties. Due to the length of time since the beginning of the pandemic, repeated cross-sectional surveys are now difficult to interpret without the use of models to account for antibody waning.

Plant viruses cause substantial losses in crop yield and quality; therefore, devising new, robust strategies to counter viral infections has important implications for agriculture. Virus inhibitory protein endoplasmic reticulum-associated interferon-inducible (Viperin) proteins are conserved antiviral proteins. Here, we identified a set of Viperin and Viperin-like proteins from multiple species and tested whether they could interfere with RNA viruses in planta . Our data from transient and stable overexpression of these proteins in Nicotiana benthamiana reveal varying levels of interference against the RNA viruses tobacco mosaic virus (TMV), turnip mosaic virus (TuMV), and potato virus x (PVX). Harnessing the potential of these proteins represents a novel avenue in plant antiviral approaches, offering a broader and more effective spectrum for application in plant biotechnology and agriculture. Identifying these proteins opens new avenues for engineering a broad range of resistance to protect crop plants against viral pathogens.