Characterization of a New Orthotospovirus from Chilli Pepper in Yunnan Province, China

Emerging challenges in the management of Orthotospoviruses in Indian agriculture

Orthotospoviruses, a genera of negative-sense ssRNA viruses transmitted by thrips, have gained significant attention in recent years due to their detrimental impact on diverse crops, causing substantial economic losses and posing threats to food security. Orthotospoviruses are characterised by a wide range of symptoms in plants, including chlorotic/necrotic spots, vein banding, and fruit deformation. Seven species, including four definite and three tentative species in the genus Orthotospovirus, have so far been documented on the crops of the Indian subcontinent. Management of Orthotospoviruses under field conditions is challenging since they have a wide host range, adaptation to versatile environmental conditions, a lack of promising resistance sources, and the ubiquitous nature of thrips and their transmission through a propagative manner. Our present review elucidates the significance, molecular biology and evolutionary relationship of Orthotospoviruses; vector population; and possible management strategies for Orthotospoviruses and their vectors in the scenario of the Indian subcontinent.

Advances and Prospects of Virus-Resistant Breeding in Tomatoes

Plant viruses are the main pathogens which cause significant quality and yield losses in tomato crops. The important viruses that infect tomatoes worldwide belong to five genera: Begomovirus, Orthotospovirus, Tobamovirus, Potyvirus, and Crinivirus. Tomato resistance genes against viruses, including Ty gene resistance against begomoviruses, Sw gene resistance against orthotospoviruses, Tm gene resistance against tobamoviruses, and Pot 1 gene resistance against potyviruses, have been identified from wild germplasm and introduced into cultivated cultivars via hybrid breeding. However, these resistance genes mainly exhibit qualitative resistance mediated by single genes, which cannot protect against virus mutations, recombination, mixed-infection, or emerging viruses, thus posing a great challenge to tomato antiviral breeding. Based on the epidemic characteristics of tomato viruses, we propose that future studies on tomato virus resistance breeding should focus on rapidly, safely, and efficiently creating broad-spectrum germplasm materials resistant to multiple viruses. Accordingly, we summarized and analyzed the advantages and characteristics of the three tomato antiviral breeding strategies, including marker-assisted selection (MAS)-based hybrid breeding, RNA interference (RNAi)-based transgenic breeding, and CRISPR/Cas-based gene editing. Finally, we highlighted the challenges and provided suggestions for improving tomato antiviral breeding in the future using the three breeding strategies.

Identification of a Common Epitope in Nucleocapsid Proteins of Euro-America Orthotospoviruses and Its Application for Tagging Proteins

The NSs protein and the nucleocapsid protein (NP) of orthotospoviruses are the major targets for serological detection and diagnosis. A common epitope of KFTMHNQIF in the NSs proteins of Asia orthotospoviruses has been applied as an epitope tag (nss-tag) for monitoring recombinant proteins. In this study, a monoclonal antibody TNP MAb against the tomato spotted wilt virus (TSWV) NP that reacts with TSWV-serogroup members of Euro-America orthotospoviruses was produced. By truncation and deletion analyses of TSWV NP, the common epitope of KGKEYA was identified and designated as the np sequence. The np sequence was successfully utilized as an epitope tag (np-tag) to monitor various proteins, including the green fluorescence protein, the coat protein of the zucchini yellow mosaic virus, and the dust mite chimeric allergen Dp25, in a bacterial expression system. The np-tag was also applied to investigate the protein-protein interaction in immunoprecipitation. In addition, when the np-tag and the nss-tag were simultaneously attached at different termini of the expressed recombinant proteins, they reacted with the corresponding MAbs with high sensitivity. Here, we demonstrated that the np sequence and TNP MAb can be effectively applied for tagging and detecting proteins and can be coupled with the nss-tag to form a novel epitope-tagging system for investigating protein-protein interactions.

Occurrence, Distribution, Evolutionary Relationships, Epidemiology, and Management of Orthotospoviruses in China

Orthotospoviruses are responsible for serious crop losses worldwide. Orthotospoviral diseases have spread rapidly in China over the past 10 years and are now found in 19 provinces. Currently, 17 Orthotospovirus species have been reported in China, including eight newly identified species from this genus. The number of new highly pathogenic Orthotospovirus strains or species has increased, likely because of the virus species diversity, the wide range of available hosts, adaptation of the viruses to different climates, and multiple transmission routes. This review describes the distribution of Orthotospovirus species, host plants, typical symptoms of infection under natural conditions, the systemic infection of host plants, spatial clustering characteristics of virus particles in host cells, and the orthotospoviral infection cycle in the field. The evolutionary relationships of orthotospoviruses isolated from China and epidemiology are also discussed. In order to effectively manage orthotospoviral disease, future research needs to focus on deciphering the underlying mechanisms of systemic infection, studying complex/mixed infections involving the same or different Orthotospovirus species or other viruses, elucidating orthotospovirus adaptative mechanisms to multiple climate types, breeding virus-resistant plants, identifying new strains and species, developing early monitoring and early warning systems for plant infection, and studying infection transmission routes.

The Plant Negative-Sense RNA Virosphere: Virus Discovery Through New Eyes

The use of high-throughput sequencing (HTS) for virus diagnostics, as well as the importance of this technology as a valuable tool for discovery of novel viruses has been extensively investigated. In this review, we consider the application of HTS approaches to uncover novel plant viruses with a focus on the negative-sense, single-stranded RNA virosphere. Plant viruses with negative-sense and ambisense RNA (NSR) genomes belong to several taxonomic families, including Rhabdoviridae, Aspiviridae, Fimoviridae, Tospoviridae, and Phenuiviridae. They include both emergent pathogens that infect a wide range of plant species, and potential endophytes which appear not to induce any visible symptoms. As a consequence of biased sampling based on a narrow focus on crops with disease symptoms, the number of NSR plant viruses identified so far represents only a fraction of this type of viruses present in the virosphere. Detection and molecular characterization of NSR viruses has often been challenging, but the widespread implementation of HTS has facilitated not only the identification but also the characterization of the genomic sequences of at least 70 NSR plant viruses in the last 7 years. Moreover, continuing advances in HTS technologies and bioinformatic pipelines, concomitant with a significant cost reduction has led to its use as a routine method of choice, supporting the foundations of a diverse array of novel applications such as quarantine analysis of traded plant materials and genetic resources, virus detection in insect vectors, analysis of virus communities in individual plants, and assessment of virus evolution through ecogenomics, among others. The insights from these advancements are shedding new light on the extensive diversity of NSR plant viruses and their complex evolution, and provide an essential framework for improved taxonomic classification of plant NSR viruses as part of the realm Riboviria. Thus, HTS-based methods for virus discovery, our ‘new eyes,’ are unraveling in real time the richness and magnitude of the plant RNA virosphere.