High Throughput Sequencing For Plant Virus Detection and Discovery

A comprehensive review and meta-analysis of recent advances in biotechnology for plant virus research and significant accomplishments in human health and the pharmaceutical industry

Secondary metabolites made by plants and used through their metabolic routes are today's most reliable and cost-effective way to make pharmaceuticals and improve health. The concept of genetic engineering is used for molecular pharming. As more people use plants as sources of nanotechnology systems, they are adding to this. These systems are made up of viruses-like particles (VLPs) and virus nanoparticles (VNPs). Due to their superior ability to be used as plant virus expression vectors, plant viruses are becoming more popular in pharmaceuticals. This has opened the door for them to be used in research, such as the production of medicinal peptides, antibodies, and other heterologous protein complexes. This is because biotechnological approaches have been linked with new bioinformatics tools. Because of the rise of high-throughput sequencing (HTS) and next-generation sequencing (NGS) techniques, it has become easier to use metagenomic studies to look for plant virus genomes that could be used in pharmaceutical research. A look at how bioinformatics can be used in pharmaceutical research is also covered in this article. It also talks about plant viruses and how new biotechnological tools and procedures have made progress in the field.

Phylogeographic analysis of Begomovirus coat and replication-associated proteins

Begomoviruses are globally distributed plant pathogens that significantly limit crop production. These viruses are traditionally described according to phylogeographic distribution and categorized into two groups: begomoviruses from the Africa, Asia, Europe and Oceania (AAEO) region and begomoviruses from the Americas. Monopartite begomoviruses are more common in the AAEO region, while bipartite viruses predominate in the Americas, where the begomoviruses lack the V2/AV2 gene involved in inter-cellular movement and RNA silencing suppression found in AAEO begomoviruses. While these features are generally accepted as lineage-defining, the number of known species has doubled due to sequence-based discovery since 2010. To re-evaluate the geographic groupings after the rapid expansion of the genus, we conducted phylogenetic analyses for begomovirus species representatives of the two longest and most conserved begomovirus proteins: the coat and replication-associated proteins. Both proteins still largely support the broad AAEO and Americas begomovirus groupings, except for sweet potato-infecting begomoviruses that form an independent, well-supported clade for their coat protein regardless of the region they were isolated from. Our analyses do not support more fine-scaled phylogeographic groupings. Monopartite and bipartite genome organizations are broadly interchanged throughout the phylogenies, and the absence of the V2/AV2 gene is highly reflective of the split between Americas and AAEO begomoviruses. We observe significant evidence of recombination within the Americas and within the AAEO region but rarely between the regions. We speculate that increased globalization of agricultural trade, the invasion of polyphagous whitefly vector biotypes and recombination will blur begomovirus phylogeographic delineations in the future.

Characterization of Two Novel Viruses Within a Complex Virome from Flowering Ginger in Hawaii

Flowering ginger (Alpinia purpurata) is economically and culturally important in Hawaii. In the past decade, a slow decline syndrome has impacted the production of this crop in the state. RNA sequencing analyses and virus indexing surveys were done on samples collected from four of the Hawaiian Islands. Viral sequences corresponding to six viruses were recovered from transcriptomic data from samples with virus-like symptoms. Canna yellow mottle virus (CaYMV, genus Badnavirus) and two novel viruses, Alpinia vein clearing virus (ApVCV, genus Ampelovirus) and Alpinia vein streaking virus (ApVSV, genus Betanucleorhabdovirus), were found at a moderate incidence in diseased plants. Conversely, three other viruses, including the two potyviruses, banana bract mosaic virus and bean common mosaic virus, and a badnavirus, banana streak GF virus, were also found but at a low incidence. Virus detection in potential insect vectors and transmission assays identified the mealybug Planococcus citri as a vector of CaYMV and ApVCV, whereas the aphid Pentalonia caladii was identified as a vector of the novel ApVSV. Both P. citri and P. caladii are common pests of flowering ginger in Hawaii. Transmission of ApVSV was achieved using P. caladii colonies either established in the laboratory or naturally feeding on infected plants, although no transmission was obtained using viruliferous aphids originally reared on taro (Colocasia esculenta). Our study provides insights into the potential association between viral infections and the observed decline symptoms of flowering ginger in Hawaii. However, more definitive studies are needed to link single or mixed viral infections with decline symptoms.

New persistent plant RNA virus carries mutations to weaken viral suppression of antiviral RNA interference

Persistent plant viruses are widespread in natural ecosystems. However, little is known about why persistent infection with these viruses may cause little or no harm to their host. Here, we discovered a new polerovirus that persistently infected wild rice plants by deep sequencing and assembly of virus-derived small-interfering RNAs (siRNAs). The new virus was named Rice tiller inhibition virus 2 (RTIV2) based on the symptoms developed in cultivated rice varieties following Agrobacterium-mediated inoculation with an infectious RTIV2 clone. We showed that RTIV2 infection induced antiviral RNA interference (RNAi) in both the wild and cultivated rice plants as well as Nicotiana benthamiana. It is known that virulent virus infection in plants depends on effective suppression of antiviral RNAi by viral suppressors of RNAi (VSRs). Notably, the P0 protein of RTIV2 exhibited weak VSR activity and carries alanine substitutions of two amino acids broadly conserved among diverse poleroviruses. Mixed infection with umbraviruses enhanced RTIV2 accumulation and/or enabled its mechanical transmission in N. benthamiana. Moreover, replacing the alanine at either one or both positions of RTIV2 P0 enhanced the VSR activity in a co-infiltration assay, and RTIV2 mutants carrying the corresponding substitutions replicated to significantly higher levels in both rice and N. benthamiana plants. Together, our findings show that as a persistent plant virus, RTIV2 carries specific mutations in its VSR gene to weaken viral suppression of antiviral RNAi. Our work reveals a new strategy for persistent viruses to maintain long-term infection by weak suppression of the host defence response.

High-Throughput Sequencing Identified Multiple Fig Viruses and Viroids Associated with Fig Mosaic Disease in Iraq

Mosaic is the most common viral disease affecting fig plants. Although the Fig mosaic virus is the leading cause of mosaic disease, other viruses are also involved. High-throughput sequencing was used to assess viral infections in fig plants with mosaic. The genomic DNA and total RNAseq of mosaic-symptomatic fig leaves were sequenced using the Illumina platform. The analysis revealed the presence of fig badnavirus 1 (FBV-1), grapevine badnavirus 1 (GBV-1), citrus exocortis viroid (CEVd), and apple dimple fruit viroid (ADFVd). The FBV-1 and GBV-1 sequences were 7,140 bp and 7,239 bp long, respectively. The two genomes encode one open reading frame containing five major protein domains. The viroids, CEVd and ADFVd, were 397 bp and 305 bp long. Phylogenetic analyses revealed a close relationship between FBV-1 and Iranian isolates of the same species, while GBV-1 was closely related to Russian grapevine badnavirus isolates (Tem64, Blu17, KDH48, and Pal9). CEVd was closely related to other Iraqi isolates, while ADFVd was strongly related to a Spanish isolate. A registered endogenous pararetrovirus, caulimovirus-Fca1, with a size of 7,556 bp, was found in the RNA transcripts with a low expression level. This integrant was also detected in the genomes of the two lines 'Horaishi' (a female line) and 'Caprifig 6085' (a male line). Phylogenetic analyses revealed that caulimovirus-Fca1 was distinct from two other clades of different endogenous virus genera.

High-Throughput Sequencing Methods for the Detection of Two Strawberry Viruses in Post-Entry Quarantine

High-throughput sequencing (HTS) technologies may be a useful tool for testing imported plant germplasm for multiple pathogens present in a sample, offering strain-generic detection not offered by most PCR-based assays. Metatranscriptomics (RNAseq) and tiled amplicon PCR (TA-PCR) were tested as HTS-based techniques to detect viruses present in low titres. Strawberry mottle virus (SMoV), an RNA virus, and strawberry vein banding virus (SVBV), a DNA virus, were selected for comparison of RNAseq and TA-PCR with quantitative PCR assays. RNAseq of plant ribosomal RNA-depleted samples of low viral titre was used to obtain datasets from 3 M to 120 M paired-end (PE) reads. RNAseq demonstrated PCR-like sensitivity, able to detect as few as 10 viral copies/µL when 60 million (M) PE reads were generated. The custom TA-PCR primer panels designed for each virus were successfully used to recover most of the reference genomes for each virus. Single- and multiple-target TA-PCR allowed the detection of viruses in samples with around 10 viral copies/µL with a minimum continuous sequence length recovery of 500 bp. The limit of detection of the HTS-based protocols described here is comparable to that of quantitative PCR assays. This work lays the groundwork for an increased flexibility in HTS detection of plant viruses.

Improving grapevine virus diagnostics: Comparative analysis of three dsRNA enrichment methods for high-throughput sequencing

The extraction of double stranded (ds) RNA is a common enrichment method for the study, characterization, and detection of RNA viruses. In addition to RNA viruses, viroids, and some DNA viruses, can also be detected from dsRNA enriched extracts which makes it an attractive method for detecting a wide range of viruses when coupled with HTS. Several dsRNA enrichment strategies have been developed. The oldest utilizes the selective binding properties of dsRNA to cellulose. More recent methods are based on the application of anti-dsRNA antibodies and viral proteins with a specific affinity for dsRNA. All three methods have been used together with HTS for plant virus detection and study. To our knowledge, this is the first comparative study of three alternative dsRNA enrichment methods for virus and viroid detection through HTS using virus-infected, and healthy grapevine test plants. Extracts were performed in triplicate using methods based on, the anti-dsRNA antibody mAb rJ2 (Millipore Sigma Canada Ltd, Oakville, ON, Canada), the B2 dsRNA binding protein, and ReliaPrep™ Resin (Promega Corporation, Madison, WI, USA). The results show that the workflows for all three methods are effectively comparable, apart from purification steps related to antibody and binding protein construct. Both the cellulose resin and dsRNA binding protein construct methods provide highly enriched dsRNA extracts suitable for HTS with the B2 method providing a 36× and the ReliaPrep™ Resin a 163× increase in dsRNA enrichment compared to the mAb rJ2 antibody. The overall consistency and cost effectiveness of the ReliaPrep™ cellulose resin-based method and the potentially simpler adaptation to robotics made it the method of choice for future transfer to a semi-automated workflow.

Recent advances and challenges in plant viral diagnostics

Accurate and timely diagnosis of plant viral infections plays a key role in effective disease control and maintaining agricultural productivity. Recent advances in the diagnosis of plant viruses have significantly expanded our ability to detect and monitor viral pathogens in agricultural crops. This review discusses the latest advances in diagnostic technologies, including both traditional methods and the latest innovations. Conventional methods such as enzyme-linked immunosorbent assay and DNA amplification-based assays remain widely used due to their reliability and accuracy. However, diagnostics such as next-generation sequencing and CRISPR-based detection offer faster, more sensitive and specific virus detection. The review highlights the main advantages and limitations of detection systems used in plant viral diagnostics including conventional methods, biosensor technologies and advanced sequence-based techniques. In addition, it also discusses the effectiveness of commercially available diagnostic tools and challenges facing modern diagnostic techniques as well as future directions for improving informed disease management strategies. Understanding the main features of available diagnostic methodologies would enable stakeholders to choose optimal management strategies against viral threats and ensure global food security.

Comparing RT-PCR of Individual Samples with High-Throughput Sequencing of Pooled Plant Samples for Field-Level Surveillance of Viruses in Blackberry and Wild Rubus

Blackberry production is increasing in the Southeastern United States with the availability of new cultivars. In addition to high production costs, growers are challenged by virus diseases. Blackberry yellow vein disease (BYVD) significantly limits blackberry production. BYVD is associated with the crinivirus blackberry yellow vein-associated virus in mixed infections with other viruses. The specific disease etiology and ecological factors underlying BYVD are not well understood and rely on the effective diagnosis of several viruses involved in the complex. In 2021, we collected samples from blackberry plants showing BYVD symptoms, asymptomatic blackberry plants, and wild Rosaceae spp. from nine farms across South Carolina, for a total of 372 individual plant samples. RNA from individual samples was isolated and pooled into sample groups (i.e., symptomatic, asymptomatic, and wild) from each farm for a total of 24 pooled samples. We sequenced the pooled RNA using Illumina and analyzed sequence profiles using the Virtool bioinformatics application. We also tested each plant for six viruses by reverse transcriptase PCR or reverse transcriptase quantitative PCR and compared plant (PCR)-level and field (high-throughput sequencing [HTS])-level data. Virtool detected 17 known viruses in the pooled samples, including 11 blackberry viruses. PCR testing was mostly consistent with HTS, with some notable disagreements for specific viruses. Our study demonstrates that HTS could be used as an efficient tool to detect viruses in bulked samples in blackberry fields, although limitations to using HTS for field-level surveillance are also discussed here.

High-Throughput Sequencing Reveals New Viroid Species in Opuntia in Mexico

In the main cactus pear (Opuntia ficus-indica)-producing region in the State of Mexico, fruit production occupies the largest cultivated area with 15,800 ha, while 900 ha are cultivated for edible young Opuntia pads ("nopalitos") which are consumed as vegetables. Two composite samples consisting of cladodes of plants for fruit production (n = 6) and another of "nopalitos" (n = 6) showing virus-like symptoms were collected. Both sample sets were subjected to high-throughput sequencing (HTS) to identify the viruses and viroids. The HTS results were verified using RT-PCR and Sanger sequencing. Subsequently, 86 samples including cladodes from "nopalitos", plants for fruit production, xoconostles, and some wild Opuntia were analyzed via RT-PCR with specific primers for the viruses and viroids previously detected via HTS. Three viruses were discovered [Opuntia virus 2 (OV2), cactus carlavirus 1 (CCV-1), and Opuntia potexvirus A (OPV-A)], along with a previously reported viroid [Opuntia viroid 1 (OVd-1)]. Additionally, two new viroids were identified, provisionally named the Mexican opuntia viroid (MOVd, genus Pospiviroid) and Opuntia viroid 2 (OVd-2, genus Apscaviroid). A phylogenetic analysis, pairwise identity comparison, and conserved structural elements analysis confirmed the classification of these two viroids as new species within the Pospiviroidae family. This is the first report of a pospiviroid and two apscaviroids infecting cactus pears in the world. Overall, this study enhances our understanding of the virome associated with cactus pears in Mexico.

Loquat (Eriobotrya japonica) Is a New Natural Host of Tomato Mosaic Virus and Citrus Exocortis Viroid

Loquat leaves exhibiting obvious yellowing, blistering, mosaic, leaf upward cupping, crinkle, and leaf narrowing were identified in Panzhihua City, Sichuan Province, China. High-throughput sequencing (HTS) with the ribo-depleted cDNA library was employed to identify the virome in the loquat samples; only tomato mosaic virus (ToMV) and citrus exocortis viroid (CEVd) were identified in the transcriptome data. The complete genome sequence of ToMV and CEVd were obtained from the loquat leaves. The full-length genome of the ToMV-loquat is 6376 nt and comprises four open reading frames (ORFs) encoding 183 kDa protein, RNA-dependent RNA polymerase (RdRp), movement protein (MP), and coat protein (CP), respectively. A pairwise identity analysis showed that the complete sequence of the ToMV-loquat had a nucleotide identity between 98.5 and 99.3% with other ToMV isolates. A phylogenetic analysis indicated that ToMV-loquat was more closely related to ToMV-IFA9 (GenBank No. ON156781). A CEVd sequence with 361 nt in length was amplified based on the HTS contigs, sequence alignment indicated CEVd-loquat had the highest identity with the strain of CEVd-Balad (GenBank No. PP869624), phylogenetic analysis showed that CEVd-loquat was more closely related to CEVd-lettuce (GenBank No. ON993891). This significant discovery marks the first documentation and characterization of ToMV and CEVd infecting loquat plants, shedding light on potential threats to loquat cultivation and providing insights for disease management strategies.

Comparative Performance Evaluation of Double-Stranded RNA High-Throughput Sequencing for the Detection of Viral Infection in Temperate Fruit Crops

There is limited information on the compared performances of biological, serological. and molecular assays with high-throughput sequencing (HTS) for viral indexing in temperate fruit crops. Here, using a range of samples of predetermined virological status, we compared two performance criteria (inclusivity and analytical sensitivity) of enzyme-linked immunosorbent assay (ELISA), molecular hybridization, reverse transcription (RT)-PCR, and double-stranded RNA (dsRNA) HTS for the detection of a total of 14 viruses (10 genera) and four viroids (three genera). When undiluted samples from individual plants were used, ELISA had the lowest performance, with an overall detection rate of 68.7%, followed by RT-PCR (82.5%) and HTS (90.7%; 100% if considering only viruses). The lower performance of RT-PCR reflected the inability to amplify some isolates as a consequence of point mutations affecting primer-binding sites. In addition, HTS identified viruses that had not been identified by other assays in nearly two-thirds of the samples. Analysis of serial dilutions of fruit tree samples allowed comparison of analytical sensitivities for various viruses. ELISA showed the lowest analytical sensitivity, but RT-PCR showed higher analytical sensitivity than HTS for most of the samples. Overall, these results confirm the superiority of HTS over biological indexing in terms of speed and inclusivity and show that while the absolute analytical sensitivity of RT-PCR tends to be higher than that of HTS, PCR inclusivity is affected by viral genetic diversity. Taken together, these results make a strong case for the implementation of HTS-based approaches in fruit tree viral testing protocols supporting quarantine and certification programs.

Occurrence, distribution, and genetic diversity of faba bean viruses in China

With worldwide cultivation, the faba bean (Vicia faba L.) stands as one of the most vital cool-season legume crops, serving as a major component of food security. China leads global faba bean production in terms of both total planting area and yield, with major production hubs in Yunnan, Sichuan, Jiangsu, and Gansu provinces. The faba bean viruses have caused serious yield losses in these production areas, but previous researches have not comprehensively investigated this issue. In this study, we collected 287 faba bean samples over three consecutive years from eight provinces/municipalities of China. We employed small RNA sequencing, RT-PCR, DNA sequencing, and phylogenetic analysis to detect the presence of viruses and examine their incidence, distribution, and genetic diversity. We identified a total of nine distinct viruses: bean yellow mosaic virus (BYMV, Potyvirus), milk vetch dwarf virus (MDV, Nanovirus), vicia cryptic virus (VCV, Alphapartitivirus), bean common mosaic virus (BCMV, Potyvirus), beet western yellows virus (BWYV, Polerovirus), broad bean wilt virus (BBWV, Fabavirus), soybean mosaic virus (SMV, Potyvirus), pea seed-borne mosaic virus (PSbMV, Potyvirus), and cucumber mosaic virus (CMV, Cucumovirus). BYMV was the predominant virus found during our sampling, followed by MDV and VCV. This study marks the first reported detection of BCMV in Chinese faba bean fields. Except for several isolates from Gansu and Yunnan provinces, our sequence analysis revealed that the majority of BYMV isolates contain highly conserved nucleotide sequences of coat protein (CP). Amino acid sequence alignment indicates that there is a conserved NAG motif at the N-terminal region of BYMV CP, which is considered important for aphid transmission. Our findings not only highlight the presence and diversity of pathogenic viruses in Chinese faba bean production, but also provide target pathogens for future antiviral resource screening and a basis for antiviral breeding.

A Novel Cryptic Virus Isolated from Galphimia spp. in Mexico

Galphimia spp. is a plant employed in traditional medicine in Mexico because of its anxiolytic and sedative effects. Viruses have been associated with different alterations in plants, although asymptomatic agents (i.e., cryptic viruses) are also known. High-throughput sequencing (HTS) allows for the detection of pathogenic and non-pathogenic viral agents in plants, including potential novel viruses. The aim of this study was to investigate the presence of viral agents in two populations of Galphimia spp. by HTS. Sequencing was conducted on an Illumina NextSeq 550 platform, and a putative novel virus was identified. Two contigs showed homology to partitiviruses, and these encoded the RNA-dependent RNA polymerase and coat protein. These proteins showed the highest identities with orthologs in the recently discovered Vitis cryptic virus. A phylogenetic analysis of both RNAs showed that the new virus clusters into the monophyletic genus Deltapartitivirus along with other plant-infecting viruses. The result of the HTS analysis was validated by conventional RT-PCR and Sanger sequencing. A novel virus was discovered in a symptomless Galphimia spp. plant and tentatively named the Galphimia cryptic virus (GCV). This is the first virus discovered in medicinal plants in Mexico.

An evaluation of nucleic acid-based molecular methods for the detection of plant viruses: a systematic review

Precise and timely diagnosis of plant viruses is a prerequisite for the implementation of efficient management strategies, considering factors like globalization of trade and climate change facilitating the spread of viruses that lead to agriculture yield losses of billions yearly worldwide. Symptomatic diagnosis alone may not be reliable due to the diverse symptoms and confusion with plant abiotic stresses. It is crucial to detect plant viruses accurately and reliably and do so with little time. A complete understanding of the various detection methods is necessary to achieve this. Enzyme-linked immunosorbent assay (ELISA), has become more popular as a method for detecting viruses but faces limitations such as antibody availability, cost, sample volume, and time. Advanced techniques like polymerase chain reaction (PCR) have surpassed ELISA with its various sensitive variants. Over the last decade, nucleic acid-based molecular methods have gained popularity and have quickly replaced other techniques, such as serological techniques for detecting plant viruses due to their specificity and accuracy. Hence, this review enables the reader to understand the strengths and weaknesses of each molecular technique starting with PCR and its variations, along with various isothermal amplification followed by DNA microarrays, and next-generation sequencing (NGS). As a result of the development of new technologies, NGS is becoming more and more accessible and cheaper, and it looks possible that this approach will replace others as a favoured approach for carrying out regular diagnosis. NGS is also becoming the method of choice for identifying novel viruses.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-024-00863-0.

Diagnosis and Characterization of Plant Viruses Using HTS to Support Virus Management and Tomato Breeding

Viral diseases pose a significant threat to tomato crops (Solanum lycopersicum L.), one of the world's most economically important vegetable crops. The limited genetic diversity of cultivated tomatoes contributes to their high susceptibility to viral infections. To address this challenge, tomato breeding programs must harness the genetic resources found in native populations and wild relatives. Breeding efforts may aim to develop broad-spectrum resistance against the virome. To identify the viruses naturally infecting 19 advanced lines, derived from native tomatoes, high-throughput sequencing (HTS) of small RNAs and confirmation with PCR and RT-PCR were used. Single and mixed infections with tomato mosaic virus (ToMV), tomato golden mosaic virus (ToGMoV), and pepper huasteco yellow vein virus (PHYVV) were detected. The complete consensus genomes of three variants of Mexican ToMV isolates were reconstructed, potentially forming a new ToMV clade with a distinct 3' UTR. The absence of reported mutations associated with resistance-breaking to ToMV suggests that the Tm-1, Tm-2, and Tm-22 genes could theoretically be used to confer resistance. However, the high mutation rates and a 63 nucleotide insertion in the 3' UTR, as well as amino acid mutations in the ORFs encoding 126 KDa, 183 KDa, and MP of Mexican ToMV isolates, suggest that it is necessary to evaluate the capacity of these variants to overcome Tm-1, Tm-2, and Tm-22 resistance genes. This evaluation, along with the characterization of advanced lines using molecular markers linked to these resistant genes, will be addressed in future studies as part of the breeding strategy. This study emphasizes the importance of using HTS for accurate identification and characterization of plant viruses that naturally infect tomato germplasm based on the consensus genome sequences. This study provides crucial insights to select appropriate disease management strategies and resistance genes and guide breeding efforts toward the development of virus-resistant tomato varieties.

Application of Biotechniques for In Vitro Virus and Viroid Elimination in Pome Fruit Crops

Sustainable production of pome fruit crops is dependent upon having virus-free planting materials. The production and distribution of plants derived from virus- and viroid-negative sources is necessary not only to control pome fruit viral diseases but also for sustainable breeding activities, as well as the safe movement of plant materials across borders. With variable success rates, different in vitro-based techniques, including shoot tip culture, micrografting, thermotherapy, chemotherapy, and shoot tip cryotherapy, have been employed to eliminate viruses from pome fruits. Higher pathogen eradication efficiencies have been achieved by combining two or more of these techniques. An accurate diagnosis that confirms complete viral elimination is crucial for developing effective management strategies. In recent years, considerable efforts have resulted in new reliable and efficient virus detection methods. This comprehensive review documents the development and recent advances in biotechnological methods that produce healthy pome fruit plants. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Viral Metatranscriptomic Analysis to Reveal the Diversity of Viruses Infecting Satsuma Mandarin (Citrus unshiu) in Korea

Citrus cultivation plays a pivotal role, making a significant contribution to global fruit production and dietary consumption. Accurate identification of viral pathogens is imperative for the effective management of plant viral disease in citrus crops. High-throughput sequencing serves as an alternative approach, enabling comprehensive pathogen identification on a large scale without requiring pre-existing information. In this study, we employed HTS to investigate viral pathogens infecting citrus in three different regions of South Korea: Jejudo (Jeju), Wando-gun (Wando), and Dangjin-si (Dangjin). The results unveiled diverse viruses and viroids that exhibited regional variations. Notably, alongside the identification of well-known citrus viruses such as satsuma dwarf virus, citrus tatter leaf virus, and citrus leaf blotch virus (CLBV), this study also uncovered several viruses and viroids previously unreported in Korean citrus. Phylogenetic analysis revealed that majority of identified viruses exhibited the closest affilations with isolates from China or Japan. However, CLBV and citrus viroid-I-LSS displayed diverse phylogenetic positions, reflecting their regional origins. This study advances our understanding of citrus virome diversity and regional dynamics through HTS, emphasizing its potential in unraveling intricate viral pathogens in agriculture. Consequently, it significantly contributes to disease management strategies, ensuring the resilience of the citrus industry.

Genomic characterization of a novel cytorhabdovirus infecting Ixeris denticulata in China

Ixeris denticulata is a perennial herbal plant with important medical and economic value. In this study, a novel rhabdovirus from I. denticulata with leaf curling and mottle symptoms was identified through next-generation sequencing and molecular cloning approaches. Based on the host species and properties of this virus, it was tentatively named "Ixeris denticulata-associated rhabdovirus" (IdaRV). IdaRV has a negative-sense RNA genome that is 12,705 nucleotides in length and has five open reading frames (ORFs) in the order 3'-nucleoprotein -phosphoprotein -movement protein -matrix protein -large RNA-dependent RNA polymerase-5'. Pairwise sequence comparisons showed that IdaRV had 42.2-53.0% sequence identity to members of the genera Cytorhabdovirus, Varicosavirus, Betanucleorhabdovirus, Gammanucleorhabdovirus, Dichorhavirus, and Alphanucleorhabdovirus in the subfamily Betarhabdovirinae. BLASTp searches indicated that putative products of ORF1, ORF2, ORF3, ORF4, and ORF5 of IdaRV are most closely related to those of rudbeckia virus 1 (RudV1, GenBank accession number ON185810), with 32.1%, 21.3%, 52.4%, 37.6%, and 57.1% amino acid sequence identity, respectively, at the protein level. Phylogenetic analysis showed that IdaRV forms a smaller branch with RudV1, which belongs to the genus Cytorhabdovirus. These results establish IdaRV as a novel rhabdovirus in the genus Cytorhabdovirus of the family Rhabdoviridae.

Metatranscriptome analysis of symptomatic bitter apple plants revealed mixed viral infections with a putative novel polerovirus

BACKGROUND

Next-generation Sequencing (NGS) combined with bioinformatic analyses constitutes a powerful approach for identifying and characterizing previously unknown viral genomes. In this study, leaf samples from bitter apple plants (Citrullus colocynthis (L.) Schrad) exhibiting symptoms such as dwarfing, leaf crinkling, and chlorosis were collected from the southern part of Kerman province, Iran.

RESULTS

Putative infecting viruses were identified through de novo assembly of sequencing reads using various tools, followed by BLAST analysis. Complete genomes for Squash vein yellowing virus (SqVYV), Citrus-associated rhabdovirus (CiaRV), and a novel polerovirus-related strain termed Bitter apple aphid-borne yellows virus (BaABYV) were assembled and characterized. Additionally, a partial genome for Watermelon mosaic virus (WMV) was assembled. The genomic organization of the BaABYV was determined to be 5'-ORF0-ORF1-ORF1,2-ORF3a-ORF3-ORF3,5-ORF4-3'. Amino acid sequence identities for inferred proteins (P0 and P1, P1,2) with known poleroviruses were found to be the 90% species delineation limit, implying that BaABYV should be considered a new member of the genus Polerovirus. Recombination events were observed in the BaABYV and WMV strains; such events were not found in the CiaRV strain.

CONCLUSIONS

Molecular evidence from this study suggests that C. colocynthis is a reservoir host of several plant viruses. Among them, BaABYV is proposed as a new member of the genus Polerovirus. Furthermore, the CiaRV strain has been reported for the first time from Iran.

Next Generation Sequencing, and Development of a Pipeline as a Tool for the Detection and Discovery of Citrus Pathogens to Facilitate Safer Germplasm Exchange

Citrus is affected by many diseases, and hence, the movement of citrus propagative materials is highly regulated in the USA. Currently used regulatory pathogen detection methods include biological and laboratory-based technologies, which are time-consuming, expensive, and have many limitations. There is an urgent need to develop alternate, rapid, economical, and reliable testing methods for safe germplasm exchange. Citrus huanglongbing (HLB) has devastated citrus industries leading to an increased need for germplasm exchanges between citrus growing regions for evaluating many potentially valuable hybrids for both HLB resistance and multilocational performance. In the present study, Next-Generation Sequencing (NGS) methods were used to sequence the transcriptomes of 21 test samples, including 15 well-characterized pathogen-positive plants. A workflow was designed in the CLC Genomics Workbench software, v 21.0.5 for bioinformatics analysis of the sequence data for the detection of pathogens. NGS was rapid and found to be a valuable technique for the detection of viral and bacterial pathogens, and for the discovery of new citrus viruses, complementary to the existing array of biological and laboratory assays. Using NGS methods, we detected beet western yellows virus, a newly reported citrus virus, and a variant of the citrus yellow vein-associated virus associated with the "fatal yellows" disease.

The Oxford Nanopore MinION as a Versatile Technology for the Diagnosis and Characterization of Emerging Plant Viruses

The emergence of novel viral epidemics that could affect major crops represents a serious threat to global food security. The early and accurate identification of the causative viral agent is the most important step for a rapid and effective response to disease outbreaks. Over the last years, the Oxford Nanopore Technologies (ONT) MinION sequencer has been proposed as an effective diagnostic tool for the early detection and identification of emerging viruses in plants, providing many advantages compared with different high-throughput sequencing (HTS) technologies. Here, we provide a step-by-step protocol that we optimized to obtain the virome of "Lamon bean" plants (Phaseolus vulgaris L.), an agricultural product with Protected Geographical Indication (PGI) in North-East of Italy, which is frequently subjected to multiple infections caused by different RNA viruses. The conversion of viral RNA in ds-cDNA enabled the use of Genomic DNA Ligation Sequencing Kit and Native Barcoding DNA Kit, which have been originally developed for DNA sequencing. This allowed the simultaneous diagnosis of both DNA- and RNA-based pathogens, providing a more versatile alternative to the use of direct RNA and/or direct cDNA sequencing kits.

Validation of High-Throughput Sequencing (HTS) for Routine Detection of Citrus Viruses and Viroids

The management of plant diseases relies on the accurate identification of pathogens that requires a robust and validated tool in terms of specificity, sensitivity, repeatability, and reproducibility. High-throughput sequencing (HTS) has become the method of choice for virus detection when either a complete viral status of a plant is required in a single assay or if an unknown viral agent is expected. To ensure that the most accurate diagnosis is made from an HTS data analysis, a standardized protocol per pathosystem is required. This chapter presents a detailed protocol for the detection of viruses and viroids infecting citrus using HTS. The protocol describes all the steps from sample processing, nucleic acid extraction, and bioinformatic analyses validated to be an efficient method for detection in this pathosystem. The protocol also includes a section on citrus tristeza virus (CTV) genotype differentiation using HTS data.

Computational Pipeline for the Detection of Plant RNA Viruses Using High-Throughput Sequencing

In this chapter, we describe a computational pipeline for the in silico detection of plant viruses by high-throughput sequencing (HTS) from total RNA samples. The pipeline is designed for the analysis of short reads generated using an Illumina platform and free-available software tools. First, we provide advice for high-quality total RNA purification, library preparation, and sequencing. The bioinformatics pipeline begins with the raw reads obtained from the sequencing machine and performs some curation steps to obtain long contigs. Contigs are blasted against a local database of reference nucleotide viral sequences to identify the viruses in the samples. Then, the search is refined by applying specific filters. We also provide the code to re-map the short reads against the viruses found to get information on sequencing depth and read coverage for each virus. No previous bioinformatics background is required, but basic knowledge of the Unix command line and R language is recommended.

Development of Rapid and Affordable Virus-Mimicking Artificial Positive Controls

A major bottleneck in the development of detection assays is the availability of positive controls. Their acquisition can be problematic, their maintenance is expensive, and without them, assays cannot be validated. Herein, we present a novel strategy for the development of virus-mimicking artificial positive controls (ViMAPCs). The time between design and application is less than 5 days, unlike alternatives which normally take several weeks to obtain and implement. The ViMAPCs provide a realistic representation of natural infection unlike alternatives and allow for an effortless recognition of laboratory-based contamination. The feasibility and adaptability of the strategy was evaluated using several RNA and DNA plant viruses. ViMAPCs can be used in diagnostics laboratories but also in the monitoring of pathogen outbreaks where rapid response is of utmost importance.

PhytoPipe: a phytosanitary pipeline for plant pathogen detection and diagnosis using RNA-seq data

BACKGROUND

Detection of exotic plant pathogens and preventing their entry and establishment are critical for the protection of agricultural systems while securing the global trading of agricultural commodities. High-throughput sequencing (HTS) has been applied successfully for plant pathogen discovery, leading to its current application in routine pathogen detection. However, the analysis of massive amounts of HTS data has become one of the major challenges for the use of HTS more broadly as a rapid diagnostics tool. Several bioinformatics pipelines have been developed to handle HTS data with a focus on plant virus and viroid detection. However, there is a need for an integrative tool that can simultaneously detect a wider range of other plant pathogens in HTS data, such as bacteria (including phytoplasmas), fungi, and oomycetes, and this tool should also be capable of generating a comprehensive report on the phytosanitary status of the diagnosed specimen.

RESULTS

We have developed an open-source bioinformatics pipeline called PhytoPipe (Phytosanitary Pipeline) to provide the plant pathology diagnostician community with a user-friendly tool that integrates analysis and visualization of HTS RNA-seq data. PhytoPipe includes quality control of reads, read classification, assembly-based annotation, and reference-based mapping. The final product of the analysis is a comprehensive report for easy interpretation of not only viruses and viroids but also bacteria (including phytoplasma), fungi, and oomycetes. PhytoPipe is implemented in Snakemake workflow with Python 3 and bash scripts in a Linux environment. The source code for PhytoPipe is freely available and distributed under a BSD-3 license.

CONCLUSIONS

PhytoPipe provides an integrative bioinformatics pipeline that can be used for the analysis of HTS RNA-seq data. PhytoPipe is easily installed on a Linux or Mac system and can be conveniently used with a Docker image, which includes all dependent packages and software related to analyses. It is publicly available on GitHub at https://github.com/healthyPlant/PhytoPipe and on Docker Hub at https://hub.docker.com/r/healthyplant/phytopipe .

Benchmarking of virome metagenomic analysis approaches using a large, 60+ members, viral synthetic community

IMPORTANCE

We report here efforts to benchmark performance of two widespread approaches for virome analysis, which target either virion-associated nucleic acids (VANA) or highly purified double-stranded RNAs (dsRNAs). This was achieved using synthetic communities of varying complexity levels, up to a highly complex community of 72 viral agents (115 viral molecules) comprising isolates from 21 families and 61 genera of plant viruses. The results obtained confirm that the dsRNA-based approach provides a more complete representation of the RNA virome, in particular, for high complexity ones. However, for viromes of low to medium complexity, VANA appears a reasonable alternative and would be the preferred choice if analysis of DNA viruses is of importance. Several parameters impacting performance were identified as well as a direct relationship between the completeness of virome description and sample sequencing depth. The strategy, results, and tools used here should prove useful in a range of virome analysis efforts.

Novel plant-associated genomoviruses from the Brazilian Cerrado biome

The discovery rate of new plant viruses has increased due to studies involving high-throughput sequencing (HTS), particularly for single-stranded DNA viruses of the family Genomoviridae. We carried out an HTS-based survey of genomoviruses in a wide range of native and exotic trees grown in the Brazilian Cerrado biome, and the complete genome sequences of two novel members of the family Genomoviridae from two distinct genera were determined. Specific primers were designed to detect these genomoviruses in individual samples. A new gemykolovirus (Tecoma stans associated gemykolovirus) was detected in Tecoma stans, and a new gemykibivirus (Ouratea duparquetiana associated gemykibivirus) was detected in Ouratea duparquetiana. A gemykrogvirus related to Gila monster associated gemykrogvirus (80% pairwise identity) was also detected in foliar samples of Trembleya parviflora. Our pilot study paves the way for a better characterization of this diverse collection of genomoviruses as well as their interactions with the associated tree species.

One-Step Reverse-Transcription Recombinase-Aided Amplification CRISPR/Cas12a-Based Lateral Flow Assay for Fast Field Screening and Accurate Differentiation of Four Major Tobamoviruses Infecting Tomato and Pepper

Several tobamoviruses cause substantial economic losses to tomato and pepper crops globally, especially the pepper mild mosaic virus (PMMoV), tomato brown rugose fruit virus (ToBRFV), tomato mosaic virus (ToMV), and tomato mottle mosaic virus (ToMMV). A fast and accurate detection method is essential for virus identification. An all-in-one reaction method combining a one-step reverse-transcription recombinase-aided amplification (RT-RAA) and CRISPR/Cas12a-based lateral flow assay in one mixture was developed to rapidly screen and accurately differentiate among these four tobamoviruses for field detection in tomato and pepper plants. With a generic RT-RAA primer set and a mix of four specific crRNAs, along with a portable metal incubator and the use of a crude extraction method, this method screened for PMMoV, ToBRFV, ToMV, and ToMMV concurrently in less than 1 h, enabling field workers to take action immediately. The accurate differentiation of these four viruses could be achieved by later adding a single specific crRNA.

Exploring Tomato Fruit Viromes through Transcriptome Data Analysis

This study delves into the complex landscape of viral infections in tomatoes (Solanum lycopersicum) using available transcriptome data. We conducted a virome analysis, revealing 219 viral contigs linked to four distinct viruses: tomato chlorosis virus (ToCV), southern tomato virus (STV), tomato yellow leaf curl virus (TYLCV), and cucumber mosaic virus (CMV). Among these, ToCV predominated in contig count, followed by STV, TYLCV, and CMV. A notable finding was the prevalence of coinfections, emphasizing the concurrent presence of multiple viruses in tomato plants. Despite generally low viral levels in fruit transcriptomes, STV emerged as the primary virus based on viral read count. We delved deeper into viral abundance and the contributions of RNA segments to replication. While initially focused on studying the impact of sound treatment on tomato fruit transcriptomes, the unexpected viral presence underscores the importance of considering viruses in plant research. Geographical variations in virome communities hint at potential forensic applications. Phylogenetic analysis provided insights into viral origins and genetic diversity, enhancing our understanding of the Korean tomato virome. In conclusion, this study advances our knowledge of the tomato virome, stressing the need for robust pest control in greenhouse-grown tomatoes and offering insights into virus management and crop protection.

Exploring virus presence in field-collected potato leaf samples using RNA sequencing

BACKGROUND

The quick and accurate identification of viruses is essential for plant disease management. Next-generation sequencing (NGS) technology may allow the discovery, detection, and identification of plant pathogens. This study adopted RNA-sequencing (RNA-Seq) technology to explore the viruses in three potato plants (S3, S4, and S6) growing under field conditions.

RESULTS

Potato-known infecting viruses, such as alfalfa mosaic virus (AMV), potato leafroll virus (PLRV), and potato virus Y (PVY), were identified using bioinformatics programs and validated using RT-PCR. The presence of these potato viruses was also confirmed by visual inspection of host symptoms. In addition, the nearly complete genome of PLRV and the complete or partial genome sequence of multipartite virus segments have been identified. Besides the three major potato viruses that BLASTn analysis revealed were present in our samples, BLASTx analysis revealed some reads are derived from other potato viruses, such as potato virus V (PVV), Andean potato latent virus (APLV), and tomato chlorosis virus (ToCV), which are not frequently reported in potato field screenings in Egypt. Other microbial agents, such as bacteria and fungi, were also identified in the examined sample sequences. Some mycovirus sequences derived from ourmia-like viruses and Alternaria alternata chrysovirus were also identified in sample S4, confirming the complexity of the potato microbiome under field conditions.

CONCLUSION

NGS quickly and accurately identifies potato plant viruses under field conditions. Implementing this technology on a larger scale is recommended to explore potato fields and imported plants, where symptoms may be absent, unspecific, or only triggered under certain conditions.

Complete Genome Characterization of Penicillimonavirus gammaplasmoparae, a Bipartite Member of the Family Mymonaviridae

In this study, we identified Plasmopara-viticola-lesion-associated mononegaambi virus 3 (recently classified as Penicillimonavirus gammaplasmoparae), a fungi-associated mymonavirus, in grapevine plants showing an unusual upward curling symptomatology on the leaves and premature decline. Mymonaviridae is a family comprising nine genera of negative-sense single-stranded RNA viruses infecting filamentous fungi, although few of them have been associated with oomycetes, plants, and insects. Although the first mymonavirus genome description was reported a decade ago, the genome organization of several genera in the family, including the genus Penicillimonavirus, has remained unclear to date. We have determined the complete genome of P. gammaplasmoparae, which represents the first complete genomic sequence for this genus. Moreover, we provide strong evidence that P. gammaplasmoparae genome is bipartite and comprises two RNA molecules of around 6150 and 4560 nt. Our results indicate that the grapevine powdery mildew pathogen, Erysiphe necator, was also present in the analyzed plants and suggest P. gammaplasmoparae could be infecting this fungus. However, whether the fungus and/or the mycovirus are associated with the symptomatology that initially prompted these efforts remains to be determined.

Investigating Variability in Viral Presence and Abundance across Soybean Seed Development Stages Using Transcriptome Analysis

Plant transcriptomes offer a valuable resource for studying viral communities (viromes). In this study, we explore how plant transcriptome data can be applied to virome research. We analyzed 40 soybean transcriptomes across different growth stages and identified six viruses: broad bean wilt virus 2 (BBWV2), brassica yellow virus (BrYV), beet western yellow virus (BWYV), cucumber mosaic virus (CMV), milk vetch dwarf virus (MDV), and soybean mosaic virus (SMV). SMV was the predominant virus in both Glycine max (GM) and Glycine soja (GS) cultivars. Our analysis confirmed its abundance in both, while BBWV2 and CMV were more prevalent in GS than GM. The viral proportions varied across developmental stages, peaking in open flowers. Comparing viral abundance measured by viral reads and fragments per kilobase of transcript per million (FPKM) values revealed insights. SMV showed similar FPKM values in GM and GS, but BBWV2 and CMV displayed higher FPKM proportions in GS. Notably, the differences in viral abundance between GM and GS were generally insignificant based on the FPKM values across developmental stages, except for the apical bud stage in four GM cultivars. We also detected MDV, a multi-segmented virus, in two GM samples, with variable proportions of its segments. In conclusion, our study demonstrates the potential of plant transcriptomes for virome research, highlighting their strengths and limitations.

New Technologies Provide Innovative Opportunities to Enhance Understanding of Major Virus Diseases Threatening Global Food Security

Plant viruses pose a continuous and serious threat to crop production worldwide, and globalization and climate change are exacerbating the establishment and rapid spread of new viruses. Simultaneously, developments in genome sequencing technology, nucleic acid amplification methods, and epidemiological modeling are providing plant health specialists with unprecedented opportunities to confront these major threats to the food security and livelihoods of millions of resource-constrained smallholders. In this perspective, we have used recent examples of integrated application of these technologies to enhance understanding of the emergence of plant viral diseases of key food security crops in low- and middle-income countries. We highlight how international funding and collaboration have enabled high-throughput sequencing-based surveillance approaches, targeted field and lab-based diagnostic tools, and modeling approaches that can be effectively used to support surveillance and preparedness against existing and emerging plant viral threats. The importance of national and international collaboration and the future role of CGIAR in further supporting these efforts, including building capabilities to make optimal use of these technologies in low- and middle-income countries, are discussed. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

In Silico Virome Analysis of Chinese Narcissus Transcriptomes Reveals Diverse Virus Species and Genetic Diversity at Different Flower Development Stages

Viromes of Chinese narcissus flowers were explored using transcriptome data from 20 samples collected at different flower development stages. Quality controlled raw data underwent de novo assembly, resulting in 5893 viral contigs that matched the seven virus species. The most abundant viruses were narcissus common latent virus (NCLV), narcissus yellow stripe virus (NYSV), and narcissus mottling-associated virus (NMaV). As flower development stages advanced, white tepal plants showed an increase in the proportion of viral reads, while the variation in viral proportion among yellow tepal plants was relatively small. Narcissus degeneration virus (NDV) dominated the white tepal samples, whereas NDV and NYSV prevailed in the yellow tepal samples. Potyviruses, particularly NDV, are the primary infectious viruses. De novo assembly generated viral contigs for five viruses, yielding complete genomes for NCLV, NDV, narcissus late season yellow virus (NLSYV), and NYSV. Phylogenetic analysis revealed genetic diversity, with distinct NCLV, NMaV, NDV, NLSYV, and NYSV groups. This study provides valuable insights into the viromes and genetic diversity of viruses in Chinese narcissus flowers.

Development of cassava common mosaic virus-based vector for protein expression and gene editing in cassava

BACKGROUND

Plant virus vectors designed for virus-mediated protein overexpression (VOX), virus-induced gene silencing (VIGS), and genome editing (VIGE) provide rapid and cost-effective tools for functional genomics studies, biotechnology applications and genome modification in plants. We previously reported that a cassava common mosaic virus (CsCMV, genus Potexvirus)-based VIGS vector was used for rapid gene function analysis in cassava. However, there are no VOX and VIGE vectors available in cassava.

RESULTS

In this study, we developed an efficient VOX vector (CsCMV2-NC) for cassava by modifying the CsCMV-based VIGS vector. Specifically, the length of the duplicated putative subgenomic promoter (SGP1) of the CsCMV CP gene was increased to improve heterologous protein expression in cassava plants. The modified CsCMV2-NC-based VOX vector was engineered to express genes encoding green fluorescent protein (GFP), bacterial phytoene synthase (crtB), and Xanthomonas axonopodis pv. manihotis (Xam) type III effector XopAO1 for viral infection tracking, carotenoid biofortification and Xam virulence effector identification in cassava. In addition, we used CsCMV2-NC to deliver single guide RNAs (gMePDS1/2) targeting two loci of the cassava phytoene desaturase gene (MePDS) in Cas9-overexpressing transgenic cassava lines. The CsCMV-gMePDS1/2 efficiently induced deletion mutations of the targeted MePDS with the albino phenotypes in systemically infected cassava leaves.

CONCLUSIONS

Our results provide a useful tool for rapid and efficient heterologous protein expression and guide RNA delivery in cassava. This expands the potential applications of CsCMV-based vector in gene function studies, biotechnology research, and precision breeding for cassava.

Molecular and Biological Characterization of Novel and Known Family Secoviridae Members Infecting Lettuce

High-throughput sequencing of two lettuces showing virus-like symptoms in France provided evidence of infection by members of the family Secoviridae. One plant (JG1) had a complex mixed infection that involved, among others, a novel waikavirus (lettuce waikavirus 1) and two isolates of a sequivirus related to lettuce mottle virus (LeMoV). The second lettuce plant (JG2) was singly infected by LeMoV. Complete genomic sequences were obtained for all four isolates and, in addition, near complete genome sequences were obtained for other LeMoV or LeMoV-related isolates (from French cultivated and wild lettuces and from a Brazilian cultivated lettuce) and for two isolates of another family Asteraceae-infecting sequivirus, dandelion yellow mosaic virus (DaYMV). Analysis of these genomic sequences allows the proposal of tentative genome organization for the various viruses and clarification of their phylogenetic relationships. Sequence and host range comparisons point to significant differences between the two sequivirus isolates identified in the JG1 plant and LeMoV isolates from France and Brazil, suggesting they belong to a novel species for which the name lettuce star mosaic virus is proposed.

Genomic analyses of a widespread blueberry virus in the United States

Screening of blueberry accessions using high throughput sequencing revealed the presence of a new virus. Genomic structure and sequence are similar to that of nectarine stem pitting associated virus (NSPaV), a member of the genus Luteovirus, family Tombusviridae. The full genome of the new luteovirus, tentatively named blueberry virus L (BlVL), was characterized and analyzed. Similar to NSPaV, BlVL does not contain readily identifiable movement proteins in any of the seven isolates sequenced. More than 600 samples collected from five states were screened and 79% were found infected, making BlVL the most widespread blueberry virus in the United States.

High-Throughput Sequencing of Grapevine in Mexico Reveals a High Incidence of Viruses including a New Member of the Genus Enamovirus

This is the first viral metagenomic analysis of grapevine conducted in Mexico. During the summer of 2021, 48 plants displaying virus-like symptoms were sampled in Queretaro, an important grapevine-producing area of Mexico, and analyzed for the presence of viruses via high-throughput sequencing (HTS). The results of HTS were verified by real-time RT-PCR following a standardized testing scheme (Protocol 2010). Fourteen different viruses were identified, including grapevine asteroid mosaic-associated virus (GAMaV), grapevine Cabernet Sauvignon reovirus (GCSV), grapevine fanleaf virus (GFLV), grapevine fleck virus (GFkV), grapevine Pinot gris virus (GPGV), grapevine red globe virus (GRGV), grapevine rupestris stem pitting-associated virus (GRSPaV), grapevine rupestris vein feathering virus (GRVFV), grapevine Syrah virus 1 (GSyV-1), grapevine virus B (GVB), and grapevine leafroll-associated viruses 1, 2, 3, 4 (GLRaV1, 2, 3, 4). Additionally, divergent variants of GLRaV4 and GFkV, and a novel Enamovirus-like virus were discovered. This is the first report of GAMaV, GCSV, GLRaV4, GPGV, GRGV, GRVFV, and GSyV-1 infecting grapevines in Mexico; the impact of these pathogens on production is unknown.

Analysis of Virus-Derived siRNAs in Strawberry Plants Co-Infected with Multiple Viruses and Their Genotypes

Plants can be infected with multiple viruses. High-throughput sequencing tools have enabled numerous discoveries of multi-strain infections, when more than one viral strain or divergent genomic variant infects a single plant. Here, we investigated small interfering RNAs (siRNAs) in a single strawberry plant co-infected with several strains of strawberry mottle virus (SMoV), strawberry crinkle virus (SCV) and strawberry virus 1 (StrV-1). A range of plants infected with subsets of the initial viral species and strains that were obtained by aphid-mediated transmission were also evaluated. Using high-throughput sequencing, we characterized the small RNA fractions associated with different genotypes of these three viruses and determined small RNA hotspot regions in viral genomes. A comparison of virus-specific siRNA (vsiRNA) abundance with relative viral concentrations did not reveal any consistent agreement. Strawberry mottle virus strains exhibiting considerable variations in concentrations were found to be associated with comparable quantities of vsiRNAs. Additionally, by estimating the specificity of siRNAs to different viral strains, we observed that a substantial pool of vsiRNAs could target all SMoV strains, while strain-specific vsiRNAs predominantly targeted rhabdoviruses, SCV and StrV-1. This highlights the intricate nature and potential interference of the antiviral response within a single infected plant when multiple viruses are present.

The Virome of Babaco (Vasconcellea × heilbornii) Expands to Include New Members of the Rhabdoviridae and Bromoviridae

Babaco (Vasconcellea × heilbornii) is a subtropical species in the Caricaceae family. The plant is native to Ecuador and represents an important crop for hundreds of families. The objective of this study was to characterize, at the genomic level, two new babaco viruses identified by high-throughput sequencing. The viruses, an ilarvirus and a nucleorhabdovirus, were found in a symptomatic babaco plant from a commercial nursery in the Azuay province of Ecuador. The tripartite genome of the new ilarvirus, provisionally named babaco ilarvirus 1 (BabIV-1), is related to subgroup 3 ilarviruses, including apple mosaic virus, apple necrotic mosaic virus, and prunus necrotic ringspot virus as the closest relatives. The genome of the nucleorhabdovirus, provisionally named babaco nucleorhabdovirus 1 (BabRV-1), showed the closest relation with joa yellow blotch-associated virus and potato yellow dwarf nucleorhabdovirus. Molecular-based detection methods found BabIV-1 and BabRV-1 in 21% and 36%, respectively, of plants surveyed in a commercial babaco nursery, highlighting the importance of enforcing virus testing and nursery certification programs for babaco.

RNA Encapsulation Mode and Evolutionary Insights from the Crystal Structure of Emaravirus Nucleoprotein

Enveloped RNA viruses are rare among plant viruses. Fimoviridae is a newly founded family of plant viruses within the Bunyavirales order that inflicts diverse crop losses worldwide. The fig mosaic virus (FMV), the representative member of the Fimoviridae family, was shown to be a causative agent for the fig mosaic disease. Like all bunyaviruses, FMV has a segmented, negative-sense, single-stranded RNA (ssRNA) genome that is encapsulated by the viral nucleoprotein (N). Here, we present high-resolution crystal structures of FMV N in its RNA-free and RNA-bound forms, revealing a "paper fortune teller" structural transition between the two states. The tightly packed tetramer of FNV N is similar to the structures of other N proteins of different members of the Bunyavirales order. In its RNA-bound form, the tetramer reorganizes to adopt a more open state that allows the accommodation of the RNA. Despite the low sequence similarity to N proteins of animal-infecting bunyaviruses, there is a striking structural resemblance between FMV N and nucleoproteins from members of the Peribunyaviridae, an animal-infecting family of viruses. This structural homology implies that enveloped plant viruses and animal-infecting viruses might have a common ancestor from which they diverged. IMPORTANCE Most insect-born viruses circulate within the Animalia kingdom, whereas plant-infecting RNA viruses are cross-kingdom pathogens. Many plant-infecting viruses cause devastating crop damage that leads to food security endangerment. The evolutionary crossroads of interkingdom circulation and infection are poorly understood. Thus, we took the structural approach to understand the similarities and differences between interkingdom-infecting viruses and viruses that circulate within one kingdom of life. Using our structures of FMV N in its free form and in complex with a single-stranded RNA (ssRNA), we dissected the mechanism by which FMV N binds to the RNA and revealed the conformational changes associated with the binding. The resemblance of our structure to N proteins from members of the Peribunyaviridae family and their recently published ribonucleoprotein (RNP) pseudoatomic resolution assembly model suggests that the FMV genome is similarly encapsulated. Thus, our finding unveils yet another bridge by which plant- and animal-infecting viruses are interconnected.

One-Step Reverse-Transcription Loop-Mediated Isothermal Amplification (RT-LAMP) Assay for the Detection of Canna Yellow Streak Virus

Canna yellow streak virus (CaYSV) is a potyvirus that causes severe damage to the ornamental plant canna in the United Kingdom and Brazil. Here, we identified CaYSV in China by isolating total RNA from an infected plant, amplifying the virus genome segments, and cloning and sequencing the amplicons. After assembly, the full-length genome of the virus was obtained and uploaded to the NCBI database. Phylogenetic analysis results showed that the Guizhou isolate (OL546222) was most closely related to the KS isolate (MG545919.1). Virus detection is essential for virus disease control but the subclinical infection of CaYSV on canna in its early development increases the difficulty of CaYSV diagnosis. The goal of this study was to develop an efficient method for detection of CaYSV. We designed the primers, optimized the reaction conditions, and finally established a one-step reverse-transcription loop-mediated isothermal amplification (RT-LAMP) method. The product of RT-LAMP can be analyzed by both agarose gel electrophoresis and visible color change. The established one-step RT-LAMP assay showed high specificity and sensitivity in detecting CaYSV. This RT-LAMP method was also applied in analysis of 61 field samples collected from Guizhou and Jiangsu Provinces. The results showed that the infection rates of CaYSV on canna samples from these two provinces were very high (63 and 96% respectively).

Identification and Molecular Characterization of a Novel Carlavirus Infecting Chrysanthemum morifolium in China

Chrysanthemum (Chrysanthemum morifolium) is an important ornamental and medicinal plant suffering from many viruses and viroids worldwide. In this study, a new carlavirus, tentatively named Chinese isolate of Carya illinoinensis carlavirus 1 (CiCV1-CN), was identified from chrysanthemum plants in Zhejiang Province, China. The genome sequence of CiCV1-CN was 8795 nucleotides (nt) in length, with a 68-nt 5'-untranslated region (UTR) and a 76-nt 3'-UTR, which contained six predicted open reading frames (ORFs) that encode six corresponding proteins of various sizes. Phylogenetic analyses based on full-length genome and coat protein sequences revealed that CiCV1-CN is in an evolutionary branch with chrysanthemum virus R (CVR) in the Carlavirus genus. Pairwise sequence identity analysis showed that, except for CiCV1, CiCV1-CN has the highest whole-genome sequence identity of 71.3% to CVR-X6. At the amino acid level, the highest identities of predicted proteins encoded by the ORF1, ORF2, ORF3, ORF4, ORF5, and ORF6 of CiCV1-CN were 77.1% in the CVR-X21 ORF1, 80.3% in the CVR-X13 ORF2, 74.8% in the CVR-X21 ORF3, 60.9% in the CVR-BJ ORF4, 90.2% in the CVR-X6 and CVR-TX ORF5s, and 79.4% in the CVR-X21 ORF6. Furthermore, we also found a transient expression of the cysteine-rich protein (CRP) encoded by the ORF6 of CiCV1-CN in Nicotiana benthamiana plants using a potato virus X-based vector, which can result in a downward leaf curl and hypersensitive cell death over the time course. These results demonstrated that CiCV1-CN is a pathogenic virus and C. morifolium is a natural host of CiCV1.

Full genome sequence of a novel iflavirus from the aster leafhopper Macrosteles fascifrons

The aster leafhopper Macrosteles fascifrons is a common insect pest that feeds on rice and other plants and may serve as a vector to transmit various viruses. Here, we discovered a novel virus from M. fascifrons using metagenomic sequencing. We obtained its complete genome sequence by contig assembly and rapid amplification of cDNA ends, and verified the genome sequence by Sanger sequencing of overlapping segments. Based on homology search and phylogenetic analysis, the new virus belongs to the family Iflaviridae and it is tentatively named "Macrosteles fascifrons iflavirus 1" (MfIV1). Excluding the poly(A) tail, the MfIV1 genome is 10,581 nucleotides in length and it is predicted to encode a polyprotein of 3119 amino acids long, which is likely further processed to several polypeptides with conserved domains, including two rhinovirus like (rhv-like) capsid domains, a cricket paralysis virus (CRPV) capsid domain, a helicase domain, and an RNA-dependent RNA polymerase (RdRp) domain. BLAST searches show that the highest amino acid sequence identity between the capsid proteins of MfIV1 and those of other reported iflaviruses is 60.22%, indicating that MfIV1 is a new member in the family Iflaviridae.

Survey of Viruses Infecting Basella alba in Hawaii

Malabar spinach plants (Basella alba, Basellaceae) with leaves exhibiting symptoms of mosaic, rugosity, and malformation were found in a community garden on Oahu, HI in 2018. Preliminary studies using enzyme-linked immunosorbent assay and reverse-transcription (RT)-PCR identified Basella rugose mosaic virus (BaRMV) in symptomatic plants. However, nucleotide sequence analysis of RT-PCR amplicons indicated that additional potyviruses were also present in the symptomatic Malabar spinach. High-throughput sequencing (HTS) analysis was conducted on ribosomal RNA-depleted composite RNA samples of potyvirus-positive plants from three locations. Assembled contigs shared sequences similar to BaRMV, chilli veinal mottle virus (ChiVMV), Alternanthera mosaic virus (AltMV), Basella alba endornavirus (BaEV), broad bean wilt virus 2 (BBWV2), and Iresine viroid 1. Virus- and viroid-specific primers were designed based on HTS sequencing results and used in RT-PCR and Sanger sequencing to confirm the presence of these viruses and the viroid. We tested 63 additional samples from six community gardens for a survey of viruses in Malabar spinach and found that 21 of them were positive for BaRMV, 57 for ChiVMV, 21 for AltMV, 19 for BaEV, and 14 for BBWV2. This is the first characterization of the virome from B. alba.

Identification and molecular characterization of a novel cytorhabdovirus from rose plants (Rosa chinensis Jacq.)

A novel negative-sense single-stranded RNA virus, tentatively named "rose-associated cytorhabdovirus" (RaCV), was identified by high-throughput sequencing. RaCV is 16,067 nucleotides in length and contains eight open reading frames (ORFs 1-8) encoding a nucleocapsid protein (N), a putative phosphoprotein (P), a putative P3 protein (P3), a putative P4 protein (P4), a putative matrix protein (M), a glycoprotein (G), a putative P7 protein (P7), and an RNA-dependent RNA polymerase (L), respectively. The coding genes are flanked by a 3' leader sequence (228 nt) and a 5' trailer sequence (251 nt) and are separated by conserved intergenic junctions (3'-AUUCUUUUUG(N)nCUN-5'). Phylogenetic analysis showed that RaCV clustered with yerba mate virus A (YmVA) within the cytorhabdovirus clade, and it exhibited low a degree of nt sequence similarity (<40% identity) to other rhabdoviruses. Amino acid sequence comparisons between the putative proteins of RaCV and the corresponding proteins of other cytorhabdoviruses showed that the sequence identity levels were far below the species demarcation cutoff of 80% for cytorhabdoviruses. These results suggest that RaCV should be classified as a new member of the genus Cytorhabdovirus.

Translating virome analyses to support biosecurity, on-farm management, and crop breeding

Virome analysis via high-throughput sequencing (HTS) allows rapid and massive virus identification and diagnoses, expanding our focus from individual samples to the ecological distribution of viruses in agroecological landscapes. Decreases in sequencing costs combined with technological advances, such as automation and robotics, allow for efficient processing and analysis of numerous samples in plant disease clinics, tissue culture laboratories, and breeding programs. There are many opportunities for translating virome analysis to support plant health. For example, virome analysis can be employed in the development of biosecurity strategies and policies, including the implementation of virome risk assessments to support regulation and reduce the movement of infected plant material. A challenge is to identify which new viruses discovered through HTS require regulation and which can be allowed to move in germplasm and trade. On-farm management strategies can incorporate information from high-throughput surveillance, monitoring for new and known viruses across scales, to rapidly identify important agricultural viruses and understand their abundance and spread. Virome indexing programs can be used to generate clean germplasm and seed, crucial for the maintenance of seed system production and health, particularly in vegetatively propagated crops such as roots, tubers, and bananas. Virome analysis in breeding programs can provide insight into virus expression levels by generating relative abundance data, aiding in breeding cultivars resistant, or at least tolerant, to viruses. The integration of network analysis and machine learning techniques can facilitate designing and implementing management strategies, using novel forms of information to provide a scalable, replicable, and practical approach to developing management strategies for viromes. In the long run, these management strategies will be designed by generating sequence databases and building on the foundation of pre-existing knowledge about virus taxonomy, distribution, and host range. In conclusion, virome analysis will support the early adoption and implementation of integrated control strategies, impacting global markets, reducing the risk of introducing novel viruses, and limiting virus spread. The effective translation of virome analysis depends on capacity building to make benefits available globally.

Molecular characterization of a novel ourmia‑like virus from the phytopathogenic fungus Botryosphaeria dothidea

Here, we describe a novel ourmia-like virus, Botryosphaeria dothidea ourmia-like virus 2 (BdOLV2), derived from the phytopathogenic fungus Botryosphaeria dothidea strain ZM180192-1 infecting maize in Henan province of China. The complete genome sequence of BdOLV2 consists of a positive-sense single-stranded RNA (+ ssRNA) segment with a length of 2,532 nucleotides (nt). The sequence contains a large open reading frame (ORF) encoding a putative RNA-dependent RNA polymerase (RdRp) consisting of 605 amino acids (aa) with a molecular mass of 68.59 kDa. This RdRp protein contains eight typical conserved motifs associated with ourmia-like viruses. BLASTp analysis revealed that the RdRp protein of BdOLV2 had the highest similarity (62.10%, 58.15%, and 55.75% identity, respectively) to a virus previously identified as "Botourmiaviridae sp.", Macrophomina phaseolina ourmia-like virus 2, and Macrophomina phaseolina ourmia-like virus 2-A. Phylogenetic analysis based on the RdRp aa sequence indicated that BdOLV2 is a new member of the genus Magoulivirus in the family Botourmiaviridae.

Brome mosaic virus detected in Kansas wheat co-infected with other common wheat viruses

Wheat breeders are developing new virus-resistant varieties; however, it is assumed that only a few viruses or well-known viruses are present in the field. New sequencing technology is allowing for better determination of natural field virus populations. For three years, 2019-2021, Kansas wheat field surveys were conducted to determine the constituents of natural field virus populations using nanopore sequencing. During analysis, brome mosaic virus (BMV) was identified for the first time in Kansas but was in association with other wheat viruses. Brome mosaic virus was identified from 29 out of 47 different Kansas counties sampled and 44% of the total samples. BMV was found co-infected with wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) in 27.8% of the samples, with WSMV only (13.9%) and co-infected with WSMV + TriMV + High Plains wheat mosaic emaravirus (HPWMoV) (13.9%). RNA genomes of Kansas BMV isolates had 99.4 to 100% nucleotide and amino acid sequence identity, respectively, to each other. RNA2a possessed relatively high divergence (π = 0.01) compared to RNA1a and RNA3a (π = 0.004). Coding regions of all BMV RNAs were considered negative for purifying selection pressure as nonsynonymous and synonymous nucleotide ratio was less than one (dNs/dS >1). The identification of BMV in Kansas virus populations adds another layer of complexity to plant breeding. This work provides information to improve tools to aid in monitoring, detecting, and determining the variation within BMV.