•MeLaV is a new ilarvirus of the subgroup 1 infecting the weed Mercurialis annua.•The virus was found with MerV1 on diseased glasshouse-grown plants in Switzerland.•Thrips tabaci is a vector of MerV1 ...and contributes to the pollen transmission of MeLaV.•MeLaV may have been mistakenly associated with a grapevine disorder in Greece.•The virus was traced in plant and bee samples across Europe, as far back as 1991.
We report the characterization of a novel tri-segmented RNA virus infecting Mercurialis annua, a common crop weed and model species in plant science. The virus, named “Mercurialis latent virus” (MeLaV) was first identified in a mixed infection with the recently described Mercurialis orthotospovirus 1 (MerV1) on symptomatic plants grown in glasshouses in Lausanne (Switzerland). Both viruses were found to be transmitted by Thrips tabaci, which presumably help the inoculation of infected pollen in the case of MeLaV. Complete genome sequencing of the latter revealed a typical ilarviral architecture and close phylogenetic relationship with members of the Ilarvirus subgroup 1. Surprisingly, a short portion of MeLaV replicase was found to be identical to the partial sequence of grapevine angular mosaic virus (GAMV) reported in Greece in the early 1990s. However, we have compiled data that challenge the involvement of GAMV in angular mosaic of grapevine, and we propose alternative causal agents for this disorder. In parallel, three highly-conserved MeLaV isolates were identified in symptomatic leaf samples in The Netherlands, including a herbarium sample collected in 1991. The virus was also traced in diverse RNA sequencing datasets from 2013 to 2020, corresponding to transcriptomic analyses of M. annua and other plant species from five European countries, as well as metaviromics analyses of bees in Belgium. Additional hosts are thus expected for MeLaV, yet we argue that infected pollen grains have likely contaminated several sequencing datasets and may have caused the initial characterization of MeLaV as GAMV.
In cellular organisms, inosine triphosphate pyrophosphatases (ITPases) prevent the incorporation of mutagenic deaminated purines into nucleic acids. These enzymes have also been detected in the ...genomes of several plant RNA viruses infecting two euphorbia species. In particular, two ipomoviruses produce replicase-associated ITPases to cope with high concentration of non-canonical nucleotides found in cassava tissues.
Using high-throughput RNA sequencing on the wild euphorbia species Mercurialis perennis, two new members of the families Potyviridae and Secoviridae were identified. Both viruses encode for a putative ITPase, and were found in mixed infection with a new partitivirid. Following biological and genomic characterization of these viruses, the origin and function of the phytoviral ITPases were investigated.
While the potyvirid was shown to be pathogenic, the secovirid and partitivirid could not be transmitted. The secovirid was found belonging to a proposed new Comovirinae genus tentatively named "Mercomovirus", which also accommodates other viruses identified through transcriptome mining, and for which an asymptomatic pollen-associated lifestyle is suspected. Homology and phylogenetic analyses inferred that the ITPases encoded by the potyvirid and secovirid were likely acquired through independent horizontal gene transfer events, forming lineages distinct from the enzymes found in cassava ipomoviruses. Possible origins from cellular organisms are discussed for these proteins. In parallel, the endogenous ITPase of M. perennis was predicted to encode for a C-terminal nuclear localization signal, which appears to be conserved among the ITPases of euphorbias but absent in other plant families. This subcellular localization is in line with the idea that nucleic acids remain protected in the nucleus, while deaminated nucleotides accumulate in the cytoplasm where they act as antiviral molecules.
Three new RNA viruses infecting M. perennis are described, two of which encoding for ITPases. These enzymes have distinct origins, and are likely required by viruses to circumvent high level of cytoplasmic non-canonical nucleotides. This putative plant defense mechanism has emerged early in the evolution of euphorbias, and seems to specifically target certain groups of RNA viruses infecting perennial hosts.
Despite the fact that
sp. are ubiquitous fungi, their viromes have been little studied. By analysing a collection of
fungi, two new partitiviruses named Cladosporium cladosporioides partitivirus 1 ...(CcPV1) and Cladosporium cladosporioides partitivirus 2 (CcPV2) co-infecting a strain of
were identified. Their complete genome consists of two monocistronic dsRNA segments (RNA1 and RNA2) with a high percentage of pairwise identity on 5' and 3' end. The RNA directed RNA polymerase (RdRp) of both viruses and the capsid protein (CP) of CcPV1 display the classic characteristics required for their assignment to the
genus. In contrast, CcPV2 RNA2 encodes for a 41 KDa CP that is unusually smaller when aligned to CPs of other viruses classified in this genus. The structural role of this protein is confirmed by electrophoresis on acrylamide gel of purified viral particles. Despite the low percentage of identity between the capsid proteins of CcPV1 and CcPV2, their three-dimensional structures predicted by AlphaFold2 show strong similarities and confirm functional proximity. Fifteen similar viral sequences of unknown function were annotated using the CcPV2 CP sequence. The phylogeny of the CP was highly consistent with the phylogeny of their corresponding RdRp, supporting the organization of
into three distinct clades despite stretching the current demarcation criteria. It is proposed that a new subgenus be created within the genus Gammapartitivirus for this new group.
Grapevine red blotch virus (GRBV) is a recently described virus that infects grapevine. Little information is available on the possible occurrence and distribution outside North America. Therefore, ...we surveyed commercial vineyards from the three major grape-growing regions in Switzerland to determine the presence or absence of GRBV. In total, 3,062 vines were analyzed by polymerase chain reaction. None of the vines tested positive for GRBV, suggesting the absence of GRBV from Swiss vineyards. We also investigated whether GRBV was present in 653 grapevine accessions in the Agroscope grapevine virus collection at Nyon, including dominantly Swiss (457) but also international accessions. Only six referential accessions were infected by GRBV, all originating from the United States, whereas all others from 10 European and 8 non-European origins tested negative. High-throughput sequencing analysis of Zinfandel A2V13, in the collection since 1985, confirmed close similarity of GRBV isolate Z_A2V13 to American isolates according to genomes deposited in GenBank. Because the Zinfandel A2V13 reference was also maintained grafted on the leafroll virus indicator Vitis vinifera 'Gamay', we evaluated the effect of GRBV on viticultural performance over a 3-year period. Our results showed clear detrimental effects of GRBV on grapevine physiology (vine vigor, leaf chlorophyll content, and gas exchange) and fruit quality. These findings underscore the importance of implementation of GRBV testing worldwide in certification and quarantine programs to prevent the dissemination of this virus.
Tomato production is an important part of the Swiss vegetable production with most tomato crops grown in greenhouses. Tomato plants are vulnerable to diseases caused by viruses, which can have ...significant impacts on crop production. This study reports the first detection of tomato fruit botch virus (ToFBV, Blunervirus solani) in Switzerland, from a tomato production site at the southern part of the Ticino region. The symptoms observed indicated presence of a viral pathogen, but tests against the most common tomato viruses were negative. Immunocapture of double-stranded RNA and its subsequent sequencing on a Flongle flowcell (Oxford Nanopore Technologies) identified the presence of ToFBV and southern tomato virus. The genome of the Swiss ToFBV isolate was very similar to that available in GenBank. Datamining of the sequence read archives found the virus in two other countries, with a highly conserved genome. With this study, there are now 12 near-complete genomes of ToFBV available, and the virus is recorded from ten countries. This study underlines the importance of continuous monitoring and research on emerging viruses in tomato production.
In this study, an extensive virome investigation was performed on a germplasm collection of pear trees (Pyrus communis L.) from the Walloon Agricultural Research Centre (Gembloux, Belgium). In ...total,128 pear trees samples were analyzed as pools using high-throughput sequencing (HTS) techniques, and/or tested individually for targeted viruses by RT-PCR. During the virome survey, a novel velarivirus was identified in several asymptomatic trees while four known viruses were detected. Bioinformatics tools were used to assemble the genome of the new virus. The pear germplasm collection from Kozjanski Park (Slovenia) and a viral collection from Agroscope (Nyon, Switzerland) were also surveyed for the new pear virus and for three known viruses (CiVA, ARWV-1, and ARWV-2) to study their prevalence and geographic distribution. In Belgium, the new velarivirus was detected by RT-PCR in six of the 99 sampled trees (6%) and citrus virus A (CiVA) in 49 (49%) of them; in Slovenia four of the six trees sampled (67%) were positive for CiVA; and in Switzerland four of the nine trees sampled (44%) were positive for CiVA and 1 (11%) for apple rubbery wood virus 1 and 2 (ARWV-1 and -2). This study, combined pooled HTS analyses to maximize the number of germplasm tested and targeted RT-PCR tests on individual samples for accurate detection. It reports and describes a new velarivirus discovered in pear trees and first detections of CiVA in Belgium, Switzerland and Slovenia, and ARWV-1 and -2 in Switzerland.
Grapevine red blotch virus (GRBV) is a recently identified virus that infects grapevine and has a severe impact on the grape industry in North America. Since the first description of the virus 8 ...years ago, clear progress has been made regarding our understanding of the GRBV pathosystem. However, questions remain regarding the origin of this pathogen and its spread outside North America, especially in Europe. In this study, we present the results of a large-scale GRBV survey in two European repositories; we targeted
Vitis
spp. accessions with diverse geographical origins. Of 816 accessions from different origins (50 different countries around the world), six accessions were infected by GRBV, all of which originated from the United States. We investigated the DNA virome of 155 grapevine accessions from the Swiss grapevine collection using high-throughput sequencing. We observed that virome of the Swiss grapevine collection was composed of several RNA viruses. In contrast, we did not detect any DNA viruses in the 155 Swiss grapevine accessions. This finding suggests that the abundance of DNA viruses infecting grapevines in Switzerland is either very low or non-existent. Our results and the findings of studies published since 2008 show that GRBV most likely originated in North America and subsequently spread to other viticultural areas in the world via unintentional movement of infected cuttings. According to our data, the most plausible scenario for the origin of GRBV is that the virus evolved from non-
Vitis vinifera
hosts and underwent a host jump to
Vitis vinifera
after its introduction to North America in the 1600s.
In Switzerland, the rape is grown mainly on the Plateau, from Geneva to Thurgovie. With 15 000 ha cultivated, it is one of the predominant crops in our rotation-culture system. The majority is ...cultivated as autumn rape, sown at the end of August. In some of our neighboring countries, such as Germany and France, viruses responsible for virosis having a high economic impact on this crop have been detected in many rape plots. To investigate on the situation in Switzerland, a survey was realized in spring and autumn 2010 by the virology and entomology groups of the Research Station Agroscope Changins-Wädenswil ACW. This study involves 11 plots dispersed on the Swiss Plateau. The results demonstrated that despite the quasi omnipresence of these high economic impact viruses, a really low level of infection was detected.
This study was designed to test the efficacy of an air treatment using ozone and relative humidity (RH) for the inactivation of airborne viruses. Four phages (φX174, PR772, MS2 and φ6) and one ...eukaryotic virus (murine norovirus MNV-1) were exposed to low ozone concentrations (1.23 ppm for phages and 0.23 ppm for MNV-1) and various levels of RH for 10 to 70 minutes. The inactivation of these viruses was then assessed to determine which of the tested conditions provided the greatest reduction in virus infectivity. An inactivation of at least two orders of magnitude for φX174, MS2 and MNV-1 was achieved with an ozone exposure of 40 minutes at 85% RH. For PR772 and φ6, exposure to the reference condition at 20% RH for 10 minutes yielded the same results. These findings suggest that ozone used at a low concentration is a powerful disinfectant for airborne viruses when combined with a high RH. Air treatment could therefore be implemented inside hospital rooms ventilated naturally.
Influenza and RSV are human viruses responsible for outbreaks in hospitals, long-term care facilities and nursing homes. The present study assessed an air treatment using ozone at two relative ...humidity conditions (RHs) in order to reduce the infectivity of airborne influenza. Bovine pulmonary surfactant (BPS) and synthetic tracheal mucus (STM) were used as aerosols protectants to better reflect the human aerosol composition. Residual ozone concentration inside the aerosol chamber was also measured. RSV’s sensitivity resulted in testing its resistance to aerosolization and sampling processes instead of ozone exposure. The results showed that without supplement and with STM, a reduction in influenza A infectivity of four orders of magnitude was obtained with an exposure to 1.70 ± 0.19 ppm of ozone at 76% RH for 80 min. Consequently, ozone could be considered as a virucidal disinfectant for airborne influenza A. RSV did not withstand the aerosolization and sampling processes required for the use of the experimental setup. Therefore, ozone exposure could not be performed for this virus. Nonetheless, this study provides great insight for the efficacy of ozone as an air treatment for the control of nosocomial influenza A outbreaks.
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