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Genome organization of potato leafroll virus (PLRV) and linear amino acid sequence of the PLRV coat protein (CP) and the overlapping P17 movement protein (17K). The position and composition of the CP mutants are identified as shaded text. The altered amino acids are in bold type. If the mutations in the CP sequence also altered the amino acid sequence of P17, the WT amino acid is underlined and bold. The mutant name used in the text is given above each shaded area.
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The coat protein (CP) of potato leafroll virus (PLRV) is the primary component of the capsid, and is a multifunctional protein known to be involved in vector transmission and virus movement within plant hosts, in addition to particle assembly. Thirteen mutations were generated in various regions of the CP and tested for their ability to affect viru...
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... of poleroviruses and luteoviruses, as well as the CP predicted secondary struc- tures (Mayo & Ziegler-Graff, 1996). Targets included amino acids that are highly conserved among known polerovirus CP sequences, mapped epitopes (Torrance, 1992) and amino acids predicted to be on the surface of the virus particle (Mayo & Ziegler-Graff, 1996) ( Fig. 1; Table 1). The CP ORF partially overlaps ORF 4 that encodes the P17 movement protein; therefore many of the mutations in CP also resulted in amino acid changes in P17 (Fig. 1, Table 1). We have previously shown that deletion of the P17 move- ment protein did not result in any observable phenotype different from a WT infection in N. ...
Context 2
... among known polerovirus CP sequences, mapped epitopes (Torrance, 1992) and amino acids predicted to be on the surface of the virus particle (Mayo & Ziegler-Graff, 1996) ( Fig. 1; Table 1). The CP ORF partially overlaps ORF 4 that encodes the P17 movement protein; therefore many of the mutations in CP also resulted in amino acid changes in P17 (Fig. 1, Table 1). We have previously shown that deletion of the P17 move- ment protein did not result in any observable phenotype different from a WT infection in N. benthamiana or N. clevelandii ( Lee et al., ...
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Citations
... Poleroviruses contain ORF0 encoding protein 0 (P0) functioning as a suppressor of gene silencing (Pazhouhandeh et al., 2006;Csorba et al., 2010), the RNAdependent RNA polymerase (RdRp) functioning as a translational fusion of ORF1 (P1) through ORF2 (P2), a multifunctional coat protein (CP, ORF3), and a readthrough domain (ORF5; Fig. 2). The CP is essential for virion formation and aphid transmission as well as virus movement (Kaplan et al., 2007;Smirnova et al., 2015). The vector specificity and intestinal tropism in the aphid have been attributed to the minor capsid protein (mCP) of the virus (Brault et al., 2005). ...
Abstract
The genus Polerovirus is currently ascribed to the family Solemoviridae. Cucurbit aphid-borne yellows virus (CABYV) was the first cucurbit-infecting polerovirus recorded in the world from France in 1988 infecting cucumber, melon, and zucchini squash plants. Subsequently, this has been documented worldwide infecting various cucurbits within a span of 30 years from its first documentation, indicating its rapid global distribution, hence gaining the status of an “emerging virus.” Globally, eight Polerovirus species have been documented to cause economically important diseases in cucurbit crops. However, the occurrence of these viruses was not known in India until the first report of CABYV in 2017. In the recent past, the incidences of cucurbit-infecting poleroviruses have been increasing worldwide in different hosts and geographic locations causing 10%–100% crop losses in several crops. However, their impact on different crops has remained to be estimated in India. This book chapter documents the up-to-date information available on the occurrence and distribution, biology, molecular biology, detection and diagnosis, epidemiology, and management aspects of the cucurbit-infecting poleroviruses in terms of global and Indian contexts as well as the future thrust areas of research investigations.
... Additionally, a Rap1 translation initiates through a peculiar internal ribosome entry site (IRES) around 1,500 nt downstream of the 5′ end of the gRNA. From sub-genomic RNA 1 (sgRNA1), a capsid protein (CP), involved in virion formation, vector transmission, and virus movement, is encoded from ORF3 (Kaplan et al., 2007;Smirnova et al., 2015). Subsequently, ORF3 extends and ribosomes incorporate one amino acid and continue to translate ORF5 into a CP-read through domain (CP-RTD) as a fusion protein of the translational fusion of ORF3 and ORF5, which is involved in vector transmission and virus movement (Peter et al., 2008;Boissinot et al., 2014;Xu et al., 2018). ...
... As mentioned earlier, PLRV belongs to poleroviruses that are exclusively vectored by aphid species (Kaplan et al., 2007). During the insect-mediated transmission and infection processes, several hosts (insects and/or plants) and Frontiers in Microbiology 10 frontiersin.org ...
Potato leafroll virus (PLRV) is a widespread and one of the most damaging viral pathogens causing significant quantitative and qualitative losses in potato worldwide. The current knowledge of the geographical distribution, standing genetic diversity and the evolutionary patterns existing among global PLRV populations is limited. Here, we employed several bioinformatics tools and comprehensively analyzed the diversity, genomic variability, and the dynamics of key evolutionary factors governing the global spread of this viral pathogen. To date, a total of 84 full-genomic sequences of PLRV isolates have been reported from 22 countries with most genomes documented from Kenya. Among all PLRV-encoded major proteins, RTD and P0 displayed the highest level of nucleotide variability. The highest percentage of mutations were associated with RTD (38.81%) and P1 (31.66%) in the coding sequences. We detected a total of 10 significantly supported recombination events while the most frequently detected ones were associated with PLRV genome sequences reported from Kenya. Notably, the distribution patterns of recombination breakpoints across different genomic regions of PLRV isolates remained variable. Further analysis revealed that with exception of a few positively selected codons, a major part of the PLRV genome is evolving under strong purifying selection. Protein disorder prediction analysis revealed that CP-RTD had the highest percentage (48%) of disordered amino acids and the majority (27%) of disordered residues were positioned at the C-terminus. These findings will extend our current knowledge of the PLRV geographical prevalence, genetic diversity, and evolutionary factors that are presumably shaping the global spread and successful adaptation of PLRV as a destructive potato pathogen to geographically isolated regions of the world.
... On the other hand, P3 has a biologically active region that plays a vital role in CP subunit interactions, plant-virus interactions and aphid-virus recognition. Furthermore, the viral particle's assembly is required for vector transmission and determines which insect vectors can transmit the virus [97][98][99]. Thus, recombination and mutation might affect critical biological functions governed by the P3 gene. ...
The genus Polerovirus contains positive-sense, single-stranded RNA plant viruses that cause significant disease in many agricultural crops, including vegetable legumes. This study aimed to identify and determine the abundance of Polerovirus species present within Tasmanian pea crops and surrounding weeds that may act as virus reservoirs. We further sought to examine the genetic diversity of TuYV, the most commonly occurring polerovirus identified. Pea and weed samples were collected during 2019–2020 between October and January from thirty-four sites across three different regions (far northwest, north, and midlands) of Tasmania and tested by RT-PCR assay, with selected samples subject to next-generation sequencing. Results revealed that the presence of polerovirus infection and the prevalence of TuYV in both weeds and pea crops varied across the three Tasmanian cropping regions, with TuYV infection levels in pea crops ranging between 0 and 27.5% of tested plants. Overall, two species members from each genus, Polerovirus and Potyvirus, one member from each of Luteovirus, Potexvirus, and Carlavirus, and an unclassified virus from the family Partitiviridae were also found as a result of NGS data analysis. Analysis of gene sequences of the P0 and P3 genes of Tasmanian TuYV isolates revealed substantial genetic diversity within the collection, with a few isolates appearing more closely aligned with BrYV isolates. Questions remain around the differentiation of TuYV and BrYV species. Phylogenetic inconsistency in the P0 and P3 ORFs supports the concept that recombination may have played a role in TuYV evolution in Tasmania. Results of the evolutionary analysis showed that the selection pressure was higher in the P0 gene than in the P3 gene, and the majority of the codons for each gene are evolving under purifying selection. Future full genome-based analyses of the genetic variations will expand our understanding of the evolutionary patterns existing among TuYV populations in Tasmania.
... Our results rather suggest that the CP region in position 93-105 is part of a structural domain that is necessary for interaction with the vector. Alternatively, disruption of the Del3 region could affect the folding in the N-terminus and prevent the correct assembly of CP structures required for transmission, as demonstrated in other virus/vector interactions [54,55]. Comparison of virus particle morphology by transmission electron microscopy revealed that wt CVYV and CVYV_CP_Del3 were indistinguishable, and virions with the expected morphology were assembled in both cases ( Figure S2). ...
Most plant viruses rely on vector transmission for their spread and specific interactions between vector and virus have evolved to regulate this relationship. The whitefly Bemisia tabaci- transmitted cucumber vein yellowing virus (CVYV; genus Ipomovirus, family Potyviridae) is endemic in the Mediterranean Basin, where it causes significant losses in cucurbit crops. In this study, the role of the coat protein (CP) of CVYV for B. tabaci transmission and plant infection was investigated using a cloned and infectious CVYV cDNA and a collection of point and deletion mutants derived from this clone. Whitefly transmission of CVYV was abolished in a deletion mutant lacking amino acids in position 93–105 of the CP. This deletion mutant caused more severe disease symptoms compared to the cDNA clone representing the wild-type (wt) virus and movement efficiency was likewise affected. Two virus mutants carrying a partially restored CP were transmissible and showed symptoms comparable to the wt virus. Collectively, our data demonstrate that the N-terminus of the CVYV CP is a determinant for transmission by the whitefly vector and is involved in plant infection and symptom expression.
... Both poleroviruses and enamoviruses contain the RNA-dependent RNA polymerase (RdRp) that is a translational fusion of ORF1 (P1) through ORF2 (P2), a coat protein (CP, ORF3), and a read-through domain (ORF5; Fig. 1). The CP is essential for virion formation and is also involved in aphid transmission and virus movement (Kaplan et al. 2007;Smirnova et al. 2015). The CP-RT protein, formed by the translational fusion of ORF3 and ORF5, has been implicated in vector transmission and virus movement (Smirnova et al. 2015). ...
... Poleroviruses are obligatorily transmitted by aphids (Kaplan et al. 2007) and during transmission and infection face evolutionary constraints imposed by factors in the insect vector, the host plant, the environment, and their interaction (Wan et al. 2015;Li et al. 2016;Nigam and Garcia-Ruiz 2020). When viruses and hosts coevolve, interactions between host and virus factors determine compatibility or incompatibility (Garcia-Ruiz 2018). ...
The polerovirus (family Solemoviridae, genus Polerovirus) genome consists of single, positive strand RNA organized in overlapping open reading frames (ORFs) that, in addition to others, code for protein 0 (P0, a gene silencing suppressor), a coat protein (CP, ORF3) and a read-through domain (ORF5) that is fused to the CP to form a CP-RT protein. The genus Polerovirus contains 26 virus species that infect a wide variety of plants from cereals to cucurbits, to peppers. Poleroviruses are transmitted by a wide range of aphid species in the genera Rhopalosiphum, Stiobion, Aphis, and Myzus. Aphid transmission is mediated both by the CP and the CP-RT. In viruses, mutational robustness and structural flexibility are necessary for maintaining functionality in genetically diverse sets of host plants and vectors. Under this scenario, within a virus genome, mutations preferentially accumulate in areas that are determinants of host adaptation or vector transmission. In this study, we profiled genomic variation in poleroviruses. Consistent with their multifunctional nature, single nucleotide variation and selection analyses showed that ORFs coding for P0 and the read-through domain within the CP-RT are the most variable and contain the highest frequency of sites under positive selection. An order/disorder analysis showed that protein P0 is not disordered. In contrast, proteins CP-RT and VPg contain areas of disorder. Disorder is a property of multifunctional proteins with multiple interaction partners. Results described here suggest that using contrasting mechanisms, P0, VPg and CP-RT mediate adaptation to host plants, to vectors, and are contributors to the broad host and vector range of poleroviruses. Profiling genetic variation across the polerovirus genome has practical applications in diagnostics, breeding for resistance, identification of susceptibility genes, and contributes to our understanding of virus interactions with their host, vectors, and environment.
... The non-propagative circulative viruses have small icosahedral particles composed of a single capsid protein, or in the case of the luteoviruses, also incorporate the capsid + readthrough domain (RTD) in some of the structural proteins (reviewed in Wilson et al. 2019). The capsid proteins are the major determinants of vector transmission specificity and this has been determined with capsid swapping experiments and deletion/mutation analysis (Briddon et al. 1990;Chay et al. 1996;Brault et al. 2000Brault et al. , 2003Brault et al. , 2005Kaplan et al. 2007;Peter et al. 2008). Virus particles are ingested during feeding on plant tissue, and for the geminiviruses the viruses enter the vector midgut at the anterior region of the whitefly and leafhopper midgut and the filter chamber region (Medina et al. 2006;Ammar et al. 2009;Wang et al. 2014). ...
Transmission of plant viruses by their arthropod vectors is mediated by specific interactions between the plant, virus and vector. Most plant viruses are transmitted horizontally by their arthropod vectors, although reoviruses, rhabdoviruses and tenuiviruses may also be vertically transmitted. This chapter highlights recent progress and longstanding questions in vector biology. Bacterial endosymbionts of vector insects play a role in vertical transmission of plant reoviruses. Non‐circulative virus transmission refers to viruses that are transiently and reversibly retained on the cuticle which lines the inner surface of the vector mouthparts. The best‐characterized virus transmitted using the capsid strategy is the type member of the genus Cucumovirus, Cucumber mosaic virus, also renowned for its wide host range. Circulative virus transmission is characterized by viral entry into the insect body at a specific region of the alimentary canal, following acquisition during insect feeding.
... CP TuYV (Brault et al., 2003) and the counterpart CP PLRV (Lee et al., 2005) were studied by point mutations in the infectious clone of each virus, agroinfection and analysis of progeny virus genome sequence, (Brault et al., 2003;Kaplan et al., 2007;Lee et al., 2005). ...
Poleroviruses are economically important plant viruses that infect cereal, vegetable and fruit crops, and cause serious yield and quality losses worldwide. In this review we summarize the current knowledge of the function and regulation of polerovirus proteins and mention the methods employed on the different bodies of research that have produced these advances. Major biochemical and biological properties of these viral proteins are discussed in the order in which their open reading frames are organized in the genome.
... Specific antibodies can also be used in combination with electron microscopy for the fast and accurate detection of viral particles. Immunosorbent electron microscopy (ISEM) consists of decorating glow discharge-treated TEM grids directly with a coating antibody or with protein A that binds the antibody and immune-immobilized viral particles from a crude tissue sap [45][46][47][48][49]. ISEM seems to be particularly useful in encapsidation/decapsidation studies, where viral particles may be scant and an enrichment process is required prior to observation [50,51]. ...
Plant viruses are obligate parasites that need to usurp plant cell metabolism in order to infect their hosts. Imaging techniques have been used for quite a long time to study plant virus–host interactions, making it possible to have major advances in the knowledge of plant virus infection cycles. The imaging techniques used to study plant–virus interactions have included light microscopy, confocal laser scanning microscopy, and scanning and transmission electron microscopies. Here, we review the use of these techniques in plant virology, illustrating recent advances in the area with examples from plant virus replication and virus plant-to-plant vertical transmission processes.
... It should be emphasized that all other parts of the chimeric virus belong to the cytoplasmic tobamovirus, with the PLRV P3 coat protein being the only polerovirus component of the chimera. It appears the PLRV CP has to be a multifunctional protein as many other virus coat proteins involved in the particle assembly [43] and long-distance viruses transport within host plants [44][45][46][47]. As known, in addition to cell-to-cell and long-distance transport within plants, viral capsid proteins play a significant role in the infection process, including symptom development and pathogenicity [48,49]. ...
A genetically engineered chimeric virus crTMV-CP-PLRV composed of the crucifer-infecting tobacco mosaic virus (crTMV) RNA and the potato leafroll virus (plrv) coat protein (CP) was obtained by agroinfiltration of Nicotiana benthamiana with the binary vector pCambia-crTMV-CPPLRV. The significant levels of the chimeric virus enabled direct visualization of crTMV-CP-PLRV in the cell and to investigate the mechanism of the pathogenesis. Localization of the crTMV-CP-PLRV in plant cells was examined by immunoblot techniques, as well as light, and transmission electron microscopy. The chimera can transfer between vascular and nonvascular tissues. The chimeric virus inoculum is capable to infect N. benthamiana mechanically. The distinguishing feature of the chimeric virus, the RNA virus with the positive genome, was found to localize in the nucleolus. We also investigated the role of the N-terminal sequence of the PLRV P3 coat protein in the cellular localization of the virus. We believe that the gene of the PLRV CP can be substituted with genes from other challenging-to-study plant pathogens to produce other useful recombinant viruses.
... The quaternary structure environments and differences in tertiary structures observed to accommodate them display classic quasi-equivalence ( Figure 1C) with small adjustments in loops forming 5-fold and quasi 6-fold interactions. Byrne et al. (2019) mapped mutations, previously shown to effect aphid transmissibility (Kaplan et al., 2007), onto their structure of PLRV and demonstrated their surface accessibility. They also showed the shortcomings of previous homology modeling of these residues in that it failed to accurately predict the locations of the changes on the authentic subunit structure determined. ...
Luteovirids rank among the most destructive viruses of economically important crops. Until now their structures have only been inferred by inadequate homology models due to their phloem-limited infection and inadequate yields. Employing virus-like particles, Byrne et al. (2019) now report near-atomic resolution structures of two family members providing important functional insights.
