Melon yellow spot virus: A Distinct Species of the Genus Tospovirus Isolated from Melon

Development and Application of Attenuated Plant Viruses as Biological Control Agents in Japan

In 1929, it was reported that yellowing symptoms caused by a tobacco mosaic virus (TMV) yellow mosaic isolate were suppressed in tobacco plants that were systemically infected with a TMV light green isolate. Similar to vaccination, the phenomenon of cross-protection involves a whole plant being infected with an attenuated virus and involves the same or a closely related virus species. Therefore, attenuated viruses function as biological control agents. In Japan, many studies have been performed on cross-protection. For example, the tomato mosaic virus (ToMV)-L11A strain is an attenuated isolate developed by researchers and shows high control efficiency against wild-type ToMV in commercial tomato crops. Recently, an attenuated isolate of zucchini yellow mosaic virus (ZYMV)-2002 was developed and registered as a biological pesticide to control cucumber mosaic disease. In addition, attenuated isolates of pepper mild mottle virus (PMMoV), cucumber mosaic virus (CMV), tobacco mild green mosaic virus (TMGMV), melon yellow spot virus (MYSV), and watermelon mosaic virus (WMV) have been developed in Japan. These attenuated viruses, sometimes called plant vaccines, can be used not only as single vaccines but also as multiple vaccines. In this review, we provide an overview of studies on attenuated plant viruses developed in Japan. We also discuss the application of the attenuated strains, including the production of vaccinated seedlings.

Double sodium channel mutation, I265T/L1014F, is possibly related to pyrethroid-resistant in Thrips palmi

Thrips palmi Karny (Thysanoptera: Thripidae) can harm a variety of agricultural crops and transmit plant viruses, causing heavy economic losses. In the Hainan province of China, pyrethroids were sprayed widely to control T. palmi, which leaded to resistance to pyrethroids in T. palmi. The bioassay has shown that the resistance ratio of T. palmi to pyrethroids increases annually. Resistance ratio to λ-cyhalothrin has increased from 10.711 to 23.321 and to cypermethrin has increased from 5.507 to 23.051 for 3 years, 2020-2022. The double mutation (I265T/L1014F) was identified from the field strain for the first time, which were located in the domains I and II of the voltage-gated sodium channel of T. palmi, respectively. The double mutation is probably the reason for the higher resistance of T. palmi in Hainan. The frequencies of the double mutation were 53.33% in HN2020, 70.00% in HN2021, and 96.67% in HN2022. Results indicated that T. palmi had developed different degrees of resistance to pyrethroids in Hainan. This study provides theoretical guidance for the use of insecticides in the field control of thrips.

Genome-Wide Association Study Reveals a New Quantitative Trait Locus in Rice Related to Resistance to Brown Planthopper Nilaparvata lugens (Stål)

Simple Summary

The brown planthopper Nilaparvata lugens (Stål) (BPH) is one of the main rice pests in Asian areas. The development of rice varieties harboring resistance genes is the most economical and effective method of managing BPH. In this study, 123 rice germplasms were identified for resistance and durable resistance by using the rice planthopper resistance identification system. Forty-two of the 123 rice varieties were classified as resistant to brown planthopper, and among them, twelve rice varieties had a long, durable resistance period. One potential durable resistance to brown planthopper locus on chromosome 2 was found by a genome-wide association study (GWAS). There are 13 candidate genes at this locus, and several of them are related to disease and pest resistance. Our study found a potential durable resistance locus to BPH, which has guiding significance for subsequent resistance breeding.

Abstract

The brown planthopper (BPH) is one of the main pests endangering rice yields. The development of rice varieties harboring resistance genes is the most economical and effective method of managing BPH. To identify new BPH resistance-related genes, a total of 123 rice varieties were assessed for resistance and durable resistance. Three varieties were immune, and nine were highly resistant to BPH. After whole-genome resequencing of all 123 varieties, 1,897,845 single nucleotide polymorphisms (SNPs) were identified. Linkage disequilibrium (LD) decay analysis showed that the average LD of the SNPs at 20 kb was 0.30 (r²) and attenuated to half value (~0.30) at a distance of about 233 kb. A genome-wide association study (GWAS) of durable resistance to BPH was conducted using the Fast-MLM model. One quantitative trait locus, identified on chromosome 2, included 13 candidate genes. Two candidate genes contained a leucine-rich repeat and CC-NBS-LRR or NB-ARC domains, which might confer resistance to pests or diseases. Interestingly, LOC_Os02g27540 was highly expressed and was induced by BPH; GWAS identified potential rice genes coding for durable resistance to BPH. This study helps to elucidate the mechanism of durable resistance to BPH in rice and provides essential genetic information for breeding and functional verification of resistant varieties.

Effects of melon yellow spot orthotospovirus infection on the preference and developmental traits of melon thrips, Thrips palmi, in cucumber

Melon yellow spot orthotospovirus (MYSV), a member of the genus Orthotospovirus, is an important virus in cucurbits. Thrips palmi is considered the most serious pest of cucurbits because it directly damages and indirectly transmits MYSV to the plant. The effects of MYSV-infected plants on the development time, fecundity, and preference of the thrips were analyzed in this study. Our results showed that the development time of male and female thrips did not differ significantly between MYSV-infected and non-infected cucumbers. The survival rate of thrips in non-infected and MYSV-infected cucumbers were not significantly different. In a non-choice assay, T. palmi adults were released on non-infected and MYSV-infected cucumbers and allowed to lay eggs. The number of hatched larvae did not significantly differ between non-infected and MYSV-infected cucumbers. In a choice assay, MYSV had no detectable effect on the number of adult thrips and preceding hatched larvae. In a pull assay, the settling rate of thrips on the released plant did not differ significantly when the adult thrips were released to non-infected or MYSV infected cucumbers for any cucumber cultivar. Based on our results, we propose that the effects of MYSV-infected cucumbers on the development time, fecundity, or preference of T. palmi may not be an important factor in MYSV spread between cucumbers.

Role of Thrips palmi and Parthenium hysterophorus pollen in active spread of tobacco streak virus in the cotton ecosystem

Tobacco streak virus incidence in the cotton field, cv.CO14 at Department of Cotton, Tamil Nadu Agricultural University (TNAU), Coimbatore, India was nearly 36.50 %. Cotton plants infected with TSV exhibits different types of symptoms, including necrotic spots, lesions, mosaic, purplish necrotic rings, square drying, veinal necrosis and drying of terminal shoots. The highly prevalent thrips species in this cotton ecosystem was established as Thrips palmi (60.00 %) by morphological (ESEM) and molecular methods (RT-PCR using mtCOI primers). The density of the alternate weed host, Parthenium hysterophorus, was 15.05 plants per m² in these fields. Association of Thrips palmi with Parthenium was confirmed, when observed under environmental scanning electron microscope (ESEM), Parthenium pollen grains (i.e., average size @ 15000X =12.94 μm) were found adhering to its body. Molecular studies through RT-PCR confirmed the presence of TSV in the leaves and pollen grains of symptomatic and symptom-free Parthenium plants collected from the cotton field (cv. CO14). Therefore, the combined role of Thrips palmi and the Parthenium pollen grains in the transmission of TSV was examined; acquiring of TSV and its presence in the body of Thrips palmi instars and adults after 72 h of AAP was convincingly demonstrated using RT-PCR, NASH and qPCR. However virus acquired thrips could not transmit the virus. Pollen from TSV infected Parthenium plants when dusted on cotton (ANKUR 2110) seedlings along with virus acquired or non-acquired thrips led to symptom development 22 days after sowing. From the study it is evident that thrips only facilitate the movement of TSV borne pollen grains, and thereby contributing to active spread of the virus.

Taxonomy of the order Bunyavirales: update 2019

In February 2019, following the annual taxon ratification vote, the order Bunyavirales was amended by creation of two new families, four new subfamilies, 11 new genera and 77 new species, merging of two species, and deletion of one species. This article presents the updated taxonomy of the order Bunyavirales now accepted by the International Committee on Taxonomy of Viruses (ICTV).

Transcriptome-wide responses of adult melon thrips (Thrips palmi) associated with capsicum chlorosis virus infection

Thrips palmi is a widely distributed major agricultural pest in the tropics and subtropics, causing significant losses in cucurbit and solanaceous crops through feeding damage and transmission of tospoviruses. Thrips palmi is a vector of capsicum chlorosis virus (CaCV) in Australia. The present understanding of transmission biology and potential effects of CaCV on T. palmi is limited. To gain insights into molecular responses to CaCV infection, we performed RNA-Seq to identify thrips transcripts that are differentially-abundant during virus infection of adults. De-novo assembly of the transcriptome generated from whole bodies of T. palmi adults generated 166,445 contigs, of which ~24% contained a predicted open reading frame. We identified 1,389 differentially-expressed (DE) transcripts, with comparable numbers up- (708) and down-regulated (681) in virus-exposed thrips compared to non-exposed thrips. Approximately 59% of these DE transcripts had significant matches to NCBI non-redundant proteins (Blastx) and Blast2GO identified provisional functional categories among the up-regulated transcripts in virus-exposed thrips including innate immune response-related genes, salivary gland and/or gut-associated genes and vitellogenin genes. The majority of the immune-related proteins are known to serve functions in lysosome activity and melanisation in insects. Most of the up-regulated oral and extra-oral digestion-associated genes appear to be involved in digestion of proteins, lipids and plant cell wall components which may indirectly enhance the likelihood or frequency of virus transmission or may be involved in the regulation of host defence responses. Most of the down-regulated transcripts fell into the gene ontology functional category of 'structural constituent of cuticle'. Comparison to DE genes responsive to tomato spotted wilt virus in Frankliniella occidentalis indicates conservation of some thrips molecular responses to infection by different tospoviruses. This study assembled the first transcriptome in the genus Thrips and provides important data to broaden our understanding of networks of molecular interactions between thrips and tospoviruses.

Antibody array in a multiwell plate format for the sensitive and multiplexed detection of important plant pathogens

The global seed market is considered to be an important industry with a total value of $10,543 million US dollars in 2012. Because plant pathogens such as bacteria and viruses cause a significant economic loss to both producers and exporters, the seed export industry urgently requires rapid, sensitive, and inexpensive testing for the pathogens to prevent disease spreading worldwide. This study developed an antibody array in a multiwell plate format to simultaneously detect four crucial plant pathogens, namely, a bacterial fruit blotch bacterium Acidovorax avenae subsp. citrulli (Aac), Chilli veinal mottle virus (ChiVMV, potyvirus), Watermelon silver mottle virus (WSMoV, tospovirus serogroup IV), and Melon yellow spot virus (MYSV, tospovirus). The capture antibodies specific to the pathogens were immobilized on each well at preassigned positions by an automatic microarrayer. The antibodies on the arrays specifically captured the corresponding pathogens present in the sample extracts. The presence of pathogens bound on the capture antibodies was subsequently detected by a cocktail of fluorescently conjugated secondary antibodies. The limits of detection of the developed antibody array for the detection of Aac, ChiVMV, WSMoV, and MYSV were 5 × 10(5) CFU/mL, 30 ng/mL, 1000 ng/mL, and 160 ng/mL, respectively, which were very similar to those of the conventional ELISA method. The antibody array in a multiwell plate format accurately detected plant pathogens in single and multiple detections. Moreover, this format enables easy handling of the assay at a higher speed of operation.

Implementation of microfluidic sandwich ELISA for superior detection of plant pathogens

Rapid and economical screening of plant pathogens is a high-priority need in the seed industry. Crop quality control and disease surveillance demand early and accurate detection in addition to robustness, scalability, and cost efficiency typically required for selective breeding and certification programs. Compared to conventional bench-top detection techniques routinely employed, a microfluidic-based approach offers unique benefits to address these needs simultaneously. To our knowledge, this work reports the first attempt to perform microfluidic sandwich ELISA for Acidovorax citrulli (Ac), watermelon silver mottle virus (WSMoV), and melon yellow spot virus (MYSV) screening. The immunoassay occurs on the surface of a reaction chamber represented by a microfluidic channel. The capillary force within the microchannel draws a reagent into the reaction chamber as well as facilitates assay incubation. Because the underlying pad automatically absorbs excess fluid, the only operation required is sequential loading of buffers/reagents. Buffer selection, antibody concentrations, and sample loading scheme were optimized for each pathogen. Assay optimization reveals that the 20-folds lower sample volume demanded by the microchannel structure outweighs the 2- to 4-folds higher antibody concentrations required, resulting in overall 5-10 folds of reagent savings. In addition to cutting the assay time by more than 50%, the new platform offers 65% cost savings from less reagent consumption and labor cost. Our study also shows 12.5-, 2-, and 4-fold improvement in assay sensitivity for Ac, WSMoV, and MYSV, respectively. Practical feasibility is demonstrated using 19 real plant samples. Given a standard 96-well plate format, the developed assay is compatible with commercial fluorescent plate readers and readily amendable to robotic liquid handling systems for completely hand-free assay automation.

Multiplex detection of plant pathogens using a microsphere immunoassay technology

Plant pathogens are a serious problem for seed export, plant disease control and plant quarantine. Rapid and accurate screening tests are urgently required to protect and prevent plant diseases spreading worldwide. A novel multiplex detection method was developed based on microsphere immunoassays to simultaneously detect four important plant pathogens: a fruit blotch bacterium Acidovorax avenae subsp. citrulli (Aac), chilli vein-banding mottle virus (CVbMV, potyvirus), watermelon silver mottle virus (WSMoV, tospovirus serogroup IV) and melon yellow spot virus (MYSV, tospovirus). An antibody for each plant pathogen was linked on a fluorescence-coded magnetic microsphere set which was used to capture corresponding pathogen. The presence of pathogens was detected by R-phycoerythrin (RPE)-labeled antibodies specific to the pathogens. The assay conditions were optimized by identifying appropriate antibody pairs, blocking buffer, concentration of RPE-labeled antibodies and assay time. Once conditions were optimized, the assay was able to detect all four plant pathogens precisely and accurately with substantially higher sensitivity than enzyme-linked immunosorbent assay (ELISA) when spiked in buffer and in healthy watermelon leaf extract. The assay time of the microsphere immunoassay (1 hour) was much shorter than that of ELISA (4 hours). This system was also shown to be capable of detecting the pathogens in naturally infected plant samples and is a major advancement in plant pathogen detection.

Genome organisation and sequence comparison suggest intraspecies incongruence in M RNA of Watermelon bud necrosis virus

Watermelon bud necrosis virus (WBNV), a member of the genus Tospovirus, family Bunyaviridae is an important viral pathogen in watermelon cultivation in India. The complete genome sequence properties of WBNV are not available. In the present study, the complete M RNA sequence and the genome organisation of a WBNV isolate infecting watermelon in Delhi (WBNV-wDel) were determined. The M RNA was 4,794 nucleotides (nt) long and potentially coded for a movement protein (NSm) of 34.22 kDa (307 amino acids) on the viral sense strand and a Gn/Gc glycoprotein precursor of 127.15 kDa (1,121 amino acids) on the complementary strand. The two open reading frames were separated by an intergenic region of 402 nt. The 5' and 3' untranslated regions were 55 and 47 nt long, respectively, containing complementary termini typical of tospoviruses. WBNV-wDel was most closely related (79.1% identity) to Groundnut bud necrosis virus, an important tospovirus that occurs in several crops in India, and was different (63.3-75.2% identity) from the other cucurbit-infecting tospoviruses known to occur in Taiwan and Japan. Sequence analysis of NSm and Gn/Gc revealed phylogenetic incongruence between WBNV-wDel and another isolate originating from central India (WBNV-Wm-Som isolate). The Wm-Som isolate showed evolutionary divergence from the wDel isolate in the Gn/Gc protein (74.6% identity) potentially due to recombination with the other tospoviruses that are known to occur in India. This is the first report of a comparison of complete sequences of M RNA of WBNV.

Serological relationship between Melon yellow spot virus and Watermelon silver mottle virus and differential detection of the two viruses in cucurbits

Melon yellow spot virus (MYSV), a tentative member of the genus Tospovirus, is considered a distinct serotype due to the lack of a serological relationship with other tospoviruses in its nucleocapsid protein (NP). Recently, a virus isolate collected from diseased watermelon in central Taiwan (MYSV-TW) was found to react with a rabbit antiserum (RAs) prepared against the NP of Watermelon silver mottle virus (WSMoV), and a monoclonal antibody (MAb) prepared against the common epitope of the NSs proteins of WSMoV-serogroup tospoviruses, but not with the WSMoV NP-specific MAb, in both enzyme-linked immunosorbent assay (ELISA) and western blotting. In this investigation, both RAs and MAb against MYSV-TW NP were produced. Results of serological tests revealed that the RAs to MYSV-TW NP reacted with the homologous antigen and the crude antigens of members of the WSMoV serogroup, including members of the formal species WSMoV and Peanut bud necrosis virus, and members of three tentative species, Watermelon bud necrosis virus, Capsicum chlorosis virus and Calla lily chlorotic spot virus. The MAb to MYSV-TW NP reacted only with the homologous antigen and the other geographic isolates of MYSV from Japan (JP) and Thailand (TH). Our results of reciprocal tests indicate that the NP and the NSs protein of MYSV are serologically related to those of WSMoV-serogroup tospoviruses. Furthermore, we show that both the MYSV NP MAb and the WSMoV NP MAb are reliable tools for identification of MYSV and WSMoV from single or mixed infection in field surveys, as verified using species-specific primers in reverse transcription-polymerase chain reaction.

Structure and genome organization of the large RNA of iris yellow spot virus (genus Tospovirus, family Bunyaviridae)

The structure and organization of the large (L) RNA of iris yellow spot virus (IYSV) was determined, and with this report, the complete genomic sequence of IYSV of the genus Tospovirus, family Bunyaviridae has been elucidated. The L RNA of IYSV was 8,880 nucleotides in length and contained a single open reading frame in the viral complementary (vc) strand. The primary translation product of 331.17 kDa shared many of the features of the viral RNA-dependent RNA polymerase (RdRp) coded by L RNAs of known tospoviruses. The 5' and 3' termini of IYSV L RNA (vc) contain two untranslated regions of 33 and 226 nucleotides, respectively, and both termini have conserved terminal nucleotides, another common feature of tospovirus genomic RNAs. Conserved motifs characteristic of RdRps of members of the family Bunyaviridae were present in the IYSV RdRp.

Characterization of tomato zonate spot virus, a new tospovirus in China

An isolate of a new tospovirus species, causing concentric zoned ringspots on fruits and necrotic lesions on leaves of infected plants, was characterised based on particle morphology, host range and serological properties. The complete nucleotide sequences of large (L), medium (M), and small (S) RNAs of this virus were found to contain 8919, 4945, and 3279 nts respectively. The L RNA encoded the RNA-dependent RNA polymerase (RdRp) (2885 aa, 332.7 kDa). The M RNA encoded a non-structural (NSm) protein (309 aa, 34.4 kDa) and a viral glycoprotein precursor (Gn/Gc) (1122 aa, 127.4 kDa). The S RNA encoded a non-structural protein (NSs) (459 aa, 51.9 kDa) and the nucleocapsid (N) protein (278 aa, 30.6 kDa). This N protein shared amino acid identities of 80.9% with those of calla lily chlorotic spot virus. Our results suggest that the virus studied here belongs to a new tospovirus species, for which the name tomato zonate spot virus is proposed.

Biological and molecular characterization of tospoviruses in Thailand

Twenty-eight isolates of tospoviruses associated with tomato, pepper, cucurbits, peanut, and Physalis plants collected from fields in different regions of Thailand were characterized. On the basis of N gene and protein sequence relationships, three tospoviruses were identified, namely Watermelon silver mottle virus (WSMoV), Capsicum chlorosis virus (CaCV), and Melon yellow spot virus (MYSV). CLUSTAL analysis of selected N protein sequences showed different isolates of CaCV in three distinct clades. Based on necrosis symptoms on tomato and their 93% identity to CaCV isolates in the other two clades, CaCV-TD8, CaCV-AIT and CaCV-KS16-Thailand tomato tospovirus were designated as CaCV-tomato necrosis strain. A phylogenetic tree based on the 413-amino-acid Gc fragment of the CaCV-Pkk isolate supported the existence of three distinct CaCV clades. Vigna unguiculata produced concentric rings useful for discriminating the Thai CaCV peanut isolates from tomato or pepper isolates. By using reverse transcription polymerase chain reaction with species-specific primers, the three tospoviruses could be detected in mixed infections in watermelon and Physalis, as well as in the bodies of thrips vectors, Thrips palmi and Scirtothrips dorsalis, collected from fields.

The glycoprotein gene of Chrysanthemum stem necrosis virus and Zucchini lethal chlorosis virus and molecular relationship with other tospoviruses

Two tospoviruses, Chrysanthemum stem necrosis virus (CSNV) and Zucchini lethal chlorosis virus (ZLCV), cause economical losses in several ornamental and vegetable crops in Brazil. The nucleocapsid gene and movement protein sequences had already been reported for both viruses, though the glycoprotein precursor gene sequence was not available. In this study, cDNA fragments (ca. 4 kb) of the M RNA 3' portion of CSNV (isolate Chry-1) and ZLCV (isolate 1038), including the complete glycoprotein precursor gene, partial NSm gene, and the entire intergenic and 3' untranslated regions, were cloned and sequenced. The sequences were assembled with the corresponding 5' region sequence (NSm gene and 5'UTR) of the same isolates to build up the complete sequence of the M RNA segment of both species. The M RNA of CSNV was 4,828 nucleotide-long, while of ZLCV 4,836 nucleotides. Both M RNA molecules comprised two ORFs in an ambisense arrangement. The vcRNA coded for the viral glycoprotein (Gn/Gc) precursor gene of CSNV and ZLCV (both with 127.5 kDa). Comparison of deduced amino acids of the CSNV and ZLCV glycoprotein precursor genes with those of other tospoviruses showed the highest identity with that of Tomato spotted wilt virus (86%) and with that of CSNV (82%), respectively. However, the nucleotide sequence of the intergenic and 3' untranslated regions of CSNV and ZLCV shared lower identities with other tospoviruses. The glycoprotein precursor gene is thought to be a good candidate as additional classification parameter for Tospovirus taxonomy. The presence of the RGD motif in both Gc proteins indicated that they are typical American tospoviruses, which was confirmed by phylogenetic analysis. The membrane topology of both glycoproteins is discussed.

The complete nucleotide sequence of a capsicum chlorosis virus isolate from Lycopersicum esculentum in Thailand

The complete nucleotide sequence of a tospovirus isolated from Lycopersicum esculentum in Thailand was determined. The L RNA comprises of 8912 nt and codes for the RNA-dependent RNA-polymerase (RdRp) (2877 aa). Two ORFs are located on the M RNA (4823 nt) encoding the non-structural (NSm) protein (308 aa) and the viral glycoprotein precursors (Gn/Gc) (1121 aa) separated by an intergenic region of 433 nt. ORFs coding for the non-structural (NSs) and nucleocapsid (N) protein, 439 aa and 275 aa, respectively, were identified on the S RNA (3477 nt) separated by an intergenic region of 1202 nt. The N protein of the Thailand isolate was most closely related to that of capsicum chlorosis virus (CaCV), sharing an amino acid sequence identity of 92.7%. Additionally, multiple sequence analyses revealed significant similarities to tospoviruses of the species Watermelon silver mottle virus and to several putative tospovirus entries in GenBank. Based on these alignments it is proposed to refer to all these different viruses as isolates of CaCV.

Serological Comparison and Molecular Characterization for Verification of Calla lily chlorotic spot virus as a New Tospovirus Species Belonging to Watermelon silver mottle virus Serogroup

ABSTRACT Calla lily chlorotic spot virus (CCSV) isolated from central Taiwan was recently identified as a tospovirus serologically but distantly related to Watermelon silver mottle virus (WSMoV). To clarify the serological relationship between the two viruses, rabbit polyclonal antibody (PAb) to CCSV and mouse monoclonal antibodies (MAbs) to WSMoV NP or CCSV NP were produced in this investigation, using purified nucleocapsid protein (NP) as immunogens. The PAb to CCSV NP reacted stronger with the homologous antigen than with the heterologous antigen, with much lower A(405) readings in indirect enzyme-linked immunosorbent assay (ELISA) and low-intensity banding in immunoblotting. MAbs produced to CCSV NP or WSMoV NP reacted specifically with the homologous antigens but not with the heterologous antigens in both ELISA and immunoblot analyses. The CCSV S RNA was determined to be 3,172 nucleotides in length, with an inverted repeat at the 5' and 3' ends and two open reading frames encoding the NP and a nonstructural (NSs) protein in an ambisense arrangement. A typical 3'-terminal sequence (5'-AUUGCUCU-3') that is shared by all members of the genus Tospovirus also is present in the CCSV S RNA. The CCSV NP and NSs protein share low amino acid identities of 20.1 to 65.1% and 19.9 to 66.1%, respectively, with those of reported tospoviruses. Phylogenetic dendrogram analysis indicates that CCSV is a distinct member in the genus Tospovirus. The results provide evidence that CCSV is a new species in the genus Tospovirus and belongs to WSMoV serogroup.

Purification and serological analyses of tospoviral nucleocapsid proteins expressed by Zucchini yellow mosaic virus vector in squash

A plant viral vector engineered from an in vivo infectious clone of Zucchini yellow mosaic virus (ZYMV) was used to express the nucleocapsid proteins (NPs) of tospoviruses in planta. The open reading frames (ORFs) of NPs of different serogroups of tospoviruses, including Tomato spotted wilt virus, Impatiens necrotic spot virus, Watermelon silver mottle virus, Peanut bud necrosis virus, and Watermelon bud necrosis virus (WBNV), were in frame inserted in between the P1 and HC-Pro genes of the ZYMV vector. Six histidine residues and an NIa protease cleavage site were added at the C-terminal region of the inserts to facilitate purification and process of free form of the expressed NPs, respectively. Approximately 1.2-2.5 mg/NPs 100 g tissues were purified from leaf extracts of zucchini squash. The expressed WBNV NP was used as an immunogen for the production of highly specific polyclonal antisera and monoclonal antibodies. The procedure provides a convenient and fast way for production of large quantities of pure NPs of tospoviruses in planta. The system also has a potential for production of any proteins of interest in cucurbits.

Tospovirus-thrips interactions

The complex and specific interplay between thrips, tospoviruses, and their shared plant hosts leads to outbreaks of crop disease epidemics of economic and social importance. The precise details of the processes underpinning the vector-virus-host interaction and their coordinated evolution increase our understanding of the general principles underlying pathogen transmission by insects, which in turn can be exploited to develop sustainable strategies for controlling the spread of the virus through plant populations. In this review, we focus primarily on recent progress toward understanding the biological processes and molecular interactions involved in the acquisition and transmission of Tospoviruses by their thrips vectors.

Serological and Molecular Characterization of Peanut chlorotic fan-spot virus, a New Species of the Genus Tospovirus

ABSTRACT To clarify the serological relationship of Peanut chlorotic fan-spot virus (PCFV) with other tospoviruses, antisera were produced against the nucleocapsid (N) proteins of this virus and tospoviruses from four serogroups including Tomato spotted wilt virus (TSWV), Impatiens necrotic spot virus (INSV), Groundnut ringspot virus (GRSV), and Watermelon silver mottle virus (WSMoV). In immunodiffusion tests, the antisera only reacted with their homologous antigens. Similar results were noticed in indirect enzyme-linked immunosorbent assay and immunoblot tests, with the exception that strong cross-reactions were observed in heterologous combinations between TSWV and GRSV. The results indicated that the N protein of PCFV is not serologically related to those of the tospoviruses from the four serogroups. To further characterize the virus, viral S double-stranded RNA was extracted from PCFV-infected Chenopodium quinoa and used for cDNA cloning and sequencing. The full-length viral strand of the S RNA was determined to be 2,833 nucleotides, with an inverted repeat at the 5' and 3' ends and two open reading frames in an ambisense arrangement. The 3'-terminal sequence (5'-AUUGCUCU-3') of the viral S RNA is identical to those of other tospoviruses, indicating that PCFV belongs to the genus Tospovirus. The N and the NSs proteins of PCFV share low amino acid identities (22.3 to 67.5% and 19.3 to 54.2%) with those of reported tospoviruses, respectively. The phylogenetic dendrogram of the N gene of PCFV compared with those of other tospoviruses indicates that PCFV is distinct from other tospoviruses. In hybridization analyses, an N gene cDNA probe of PCFV did not react with viral RNAs of TSWV, GRSV, INSV, and WSMoV, and vice versa. Thus, based on these results, we conclude that PCFV is a new tospovirus species.

RT-PCR for detecting five distinct Tospovirus species using degenerate primers and dsRNA template

RT-PCR procedures for detection of multiple species of tospovirus from plant tissues were investigated. Downstream primers were designated from the 3' untranslated sequences of the S RNA. An upstream primer was designated from the degenerated sequences of the nucleocapsid protein. Approximately 450 bp DNA fragments were detected when Tomato spotted wilt virus (TSWV)- or Impatiens necrotic spot virus (INSV)- infected tissues were examined. Approximately 350 bp DNA fragments were detected when Watermelon silver mottle virus (WSMoV)- or Melon yellow spot virus (MYSV)-infected tissues were examined. Template RNA was extracted using CF 11 cellulose powder, and nonspecific amplification became unnoticeable when double-stranded RNA was used. The amplified fragments of WSMoV were differentiated from those of MYSV by AluI or TaqI digestion. The amplified fragments of TSWV were differentiated from those of INSV by DraI or HindIII digestion. An alstroemeria plant that was infected with an unidentified tospovirus was also examined, and a 350 bp fragment that was 97% identical to Iris yellow spot virus was detected. This method, therefore, detected at least five distinct Tospovirus species.