Tobacco Rattle Virus Infection Research Articles

Plant Poly(ADP-Ribose) Polymerase 1 Is a Potential Mediator of Cross-Talk between the Cajal Body Protein Coilin and Salicylic Acid-Mediated Antiviral Defence.

The nucleolus and Cajal bodies (CBs) are sub-nuclear domains with well-known roles in RNA metabolism and RNA-protein assembly. However, they also participate in other important aspects of cell functioning. This study uncovers a previously unrecognised mechanism by which these bodies and their components regulate host defences against pathogen attack. We show that the CB protein coilin interacts with poly(ADP-ribose) polymerase 1 (PARP1), redistributes it to the nucleolus and modifies its function, and that these events are accompanied by substantial increases in endogenous concentrations of salicylic acid (SA), activation of SA-responsive gene expression and callose deposition leading to the restriction of tobacco rattle virus (TRV) systemic infection. Consistent with this, we also find that treatment with SA subverts the negative effect of the pharmacological PARP inhibitor 3-aminobenzamide (3AB) on plant recovery from TRV infection. Our results suggest that PARP1 could act as a key molecular actuator in the regulatory network which integrates coilin activities as a stress sensor for virus infection and SA-mediated antivirus defence.

Simplifying plant gene silencing and genome editing logistics by a one-Agrobacterium system for simultaneous delivery of multipartite virus vectors.

Viral vectors provide a quick and effective way to express exogenous sequences in eukaryotic cells and to engineer eukaryotic genomes through the delivery of CRISPR/Cas components. Here, we present JoinTRV, an improved vector system based on tobacco rattle virus (TRV) that simplifies gene silencing and genome editing logistics. Our system consists of two mini T-DNA vectors from which TRV RNA1 (pLX-TRV1) and an engineered version of TRV RNA2 (pLX-TRV2) are expressed. The two vectors have compatible origins that allow their cotransformation and maintenance into a single Agrobacterium cell, as well as their simultaneous delivery to plants by a one-Agrobacterium/two-vector approach. The JoinTRV vectors are substantially smaller than those of any known TRV vector system, and pLX-TRV2 can be easily customized to express desired sequences by one-step digestion-ligation and homology-based cloning. The system was successfully used in Nicotiana benthamiana for launching TRV infection, for recombinant protein production, as well as for robust virus-induced gene silencing (VIGS) of endogenous transcripts using bacterial suspensions at low optical densities. JoinTRV-mediated delivery of single-guide RNAs in a Cas9 transgenic host allowed somatic cell editing efficiencies of ≈90%; editing events were heritable and >50% of the progeny seedlings showed mutations at the targeted loci.

Promoting virus-induced gene silencing of pepper genes by a heterologous viral silencing suppressor.

Pepper is an important vegetable cultivated worldwide. Pepper fruits accumulate unique metabolites, capsanthin and capsaicin, which are important raw materials for natural pigment and medicine. Pepper plants are rich in genetic diversity and are attractive subjects for fruit developmental studies. The release of pepper reference genomes provided key genetic information for dissecting function of pepper genes underlying various interesting phenotypes (Kim et al., 2014; Qin et al., 2014). However, due to the difficulty in transformation, dissecting genetic mechanisms in pepper remained technically challenging.

Rapid, high efficiency virus-mediated mutant complementation and gene silencing in Antirrhinum

BackgroundAntirrhinum (snapdragon) species are models for genetic and evolutionary research but recalcitrant to genetic transformation, limiting use of transgenic methods for functional genomics. Transient gene expression from viral vectors and virus-induced gene silencing (VIGS) offer transformation-free alternatives. Here we investigate the utility of Tobacco rattle virus (TRV) for homologous gene expression in Antirrhinum and VIGS in Antirrhinum and its relative Misopates.ResultsA. majus proved highly susceptible to systemic TRV infection. TRV carrying part of the Phytoene Desaturase (PDS) gene triggered efficient PDS silencing, visible as tissue bleaching, providing a reporter for the extent and location of VIGS. VIGS was initiated most frequently in young seedlings, persisted into inflorescences and flowers and was not significantly affected by the orientation of the homologous sequence within the TRV genome. Its utility was further demonstrated by reducing expression of two developmental regulators that act either in the protoderm of young leaf primordia or in developing flowers. The effects of co-silencing PDS and the trichome-suppressing Hairy (H) gene from the same TRV genome showed that tissue bleaching provides a useful marker for VIGS of a second target gene acting in a different cell layer. The ability of TRV-encoded H protein to complement the h mutant phenotype was also tested. TRV carrying the native H coding sequence with PDS to report infection failed to complement h mutations and triggered VIGS of H in wild-type plants. However, a sequence with 43% synonymous substitutions encoding H protein, was able to complement the h mutant phenotype when expressed without a PDS VIGS reporter.ConclusionsWe demonstrate an effective method for VIGS in the model genus Antirrhinum and its relative Misopates that works in vegetative and reproductive tissues. We also show that TRV can be used for complementation of a loss-of-function mutation in Antirrhinum. These methods make rapid tests of gene function possible in these species, which are difficult to transform genetically, and opens up the possibility of using additional cell biological and biochemical techniques that depend on transgene expression.

Elimination of Tobacco rattle virus from viruliferous Paratrichodorus allius in greenhouse pot experiments through cultivation of castle russet.

Corky ringspot (CRS) is a widespread potato tuber necrotic disease caused by Tobacco rattle virus (TRV) infection. In the Pacific Northwest, this virus is transmitted by the stubby root nematode (SRN) within the genus Paratrichodorus. Remediating CRS affected fields is a major challenge that can be mitigated by growing plant varieties that are resistant to TRV infection. Growing alfalfa has been shown to reduce TRV levels in CRS infested fields over time but the development of a potato cultivar with these same capabilities would be of great economic benefit to potato growers. Castle Russet is a new potato clone that does not develop symptoms of CRS disease. To assess its ability to reduce soil virus load, Castle Russet, tobacco var. “Samsun NN”, alfalfa var. “Vernema”, and Russet Burbank potato were grown for a period of 1 to 3 months in soils containing viruliferous SRN populations at two different inoculation pressures (60 nematodes/pot and 1060 nematodes/pot) in greenhouse pot experiments. SRN population size and the presence of TRV were assessed over several months post inoculation. Results indicate that plant host and length of exposure significantly influence SRN population dynamics, whereas the TRV infection status of bait plants was significantly affected by both of these factors as well as inoculation pressure. These results suggest that both alfalfa var. “Vernema” and Castle Russet are resistant to TRV infection and may potentially be used to eliminate the virus from fields affected by CRS.

Lady’s Slipper Orchid and Hydrangea: New Ornamental Hosts of Tobacco Rattle Virus (TRV) in Minnesota

The lady’s slipper orchids are a subfamily encompassing over 160 species, including the state flower of Minnesota, Cypripedium reginae. Hydrangea is a genus of about 75 species of shrubs and trees that are popular in perennial gardens. Chlorotic and necrotic foliar symptoms were observed in lady’s slipper orchid and Hydrangea arborescens on plants in St. Paul, Minnesota. From partially purified extracts, virus particles resembling those of tobacco rattle virus (TRV) were observed. TRV-specific primers amplified products from both hydrangea and lady’s slipper and were then sequenced. The sequences matched published TRV sequences with 99% identity, confirming the presence of the virus. TRV has a broad host range including ornamental, vegetable, and weed hosts. This is the first report of TRV infection in both lady’s slipper and hydrangea in Minnesota and the United States.

Interaction of a plant virus protein with the signature Cajal body protein coilin facilitates salicylic acid‐mediated plant defence responses

In addition to well-known roles in RNA metabolism, the nucleolus and Cajal bodies (CBs), both located within the nucleus, are involved in plant responses to biotic and abiotic stress. Previously we showed that plants in which expression of the CB protein coilin is downregulated are more susceptible to certain viruses including tobacco rattle virus (TRV), suggesting a role of coilin in antiviral defence. Experiments with coilin-deficient plants and the deletion mutant of the TRV 16K protein showed that both 16K and coilin are required for restriction of systemic TRV infection. The potential mechanisms of coilin-mediated antiviral defence were elucidated via experiments involving co-immunoprecipitation, use of NahG transgenic plants deficient in salicylic acid (SA) accumulation, measurement of endogenous SA concentrations and assessment of SA-responsive gene expression. Here we show that TRV 16K interacts with and relocalizes coilin to the nucleolus. In wild-type plants these events are accompanied by activation of SA-responsive gene expression and restriction of TRV systemic infection. By contrast, viral systemic spread was enhanced in NahG plants, implicating SA in these processes. Our findings suggest that coilin is involved in plant defence, responding to TRV infection by recognition of the TRV-encoded 16K protein and activating SA-dependent defence pathways.

Crosstalk between epigenetic silencing and infection by tobacco rattle virus in Arabidopsis

SummaryDNA methylation is an important epigenetic mechanism for controlling innate immunity against microbial pathogens in plants. Little is known, however, about the manner in which viral infections interact with DNA methylation pathways. Here we investigate the crosstalk between epigenetic silencing and viral infections in Arabidopsis inflorescences. We found that tobacco rattle virus (TRV) causes changes in the expression of key transcriptional gene silencing factors with RNA‐directed DNA methylation activities that coincide with changes in methylation at the whole genome level. Viral susceptibility/resistance was altered in DNA (de)methylation‐deficient mutants, suggesting that DNA methylation is an important regulatory system controlling TRV proliferation. We further show that several transposable elements (TEs) underwent transcriptional activation during TRV infection, and that TE regulation likely involved both DNA methylation‐dependent and ‐independent mechanisms. We identified a cluster of disease resistance genes regulated by DNA methylation in infected plants that were enriched for TEs in their promoters. Interestingly, TEs and nearby resistance genes were co‐regulated in TRV‐infected DNA (de)methylation mutants. Our study shows that DNA methylation contributes to modulate the outcome of viral infections in Arabidopsis, and opens up new possibilities for exploring the role of TE regulation in antiviral defence.

Molecular and Biochemical Examination of Spraing Disease in Potato Tuber in Response to Tobacco rattle virus Infection.

Field-grown tubers of potato were examined for infection by Tobacco rattle virus (TRV) and consequent production of corky ringspot or spraing symptoms. A microarray study identified genes that are differentially expressed in tuber tissue in response to TRV infection and to spraing production, suggesting that hypersensitive response (HR) pathways are activated in spraing-symptomatic tubers. This was confirmed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) of a selected group of HR-related genes and by histochemical staining of excised tuber tissue with spraing symptoms. qRT-PCR of TRV in different regions of the same tuber slice showed that nonsymptomatic areas contained higher levels of virus relative to spraing-symptomatic areas. This suggests that spraing formation is associated with an active plant defense that reduces the level of virus in the infected tuber. Expression of two of the same plant defense genes was similarly upregulated in tubers that were infected with Potato mop-top virus, a virus that also induces spraing formation.

Virus-induced alterations in primary metabolism modulate susceptibility to Tobacco rattle virus in Arabidopsis.

During compatible virus infections, plants respond by reprogramming gene expression and metabolite content. While gene expression studies are profuse, our knowledge of the metabolic changes that occur in the presence of the virus is limited. Here, we combine gene expression and metabolite profiling in Arabidopsis (Arabidopsis thaliana) infected with Tobacco rattle virus (TRV) in order to investigate the influence of primary metabolism on virus infection. Our results revealed that primary metabolism is reconfigured in many ways during TRV infection, as reflected by significant changes in the levels of sugars and amino acids. Multivariate data analysis revealed that these alterations were particularly conspicuous at the time points of maximal accumulation of TRV, although infection time was the dominant source of variance during the process. Furthermore, TRV caused changes in lipid and fatty acid composition in infected leaves. We found that several Arabidopsis mutants deficient in branched-chain amino acid catabolism or fatty acid metabolism possessed altered susceptibility to TRV. Finally, we showed that increments in the putrescine content in TRV-infected plants correlated with enhanced tolerance to freezing stress in TRV-infected plants and that impairment of putrescine biosynthesis promoted virus multiplication. Our results thus provide an interesting overview for a better understanding of the relationship between primary metabolism and virus infection.

Virus-induced gene silencing for comparative functional studies in Gladiolus hybridus

Functional analysis of genes in gladiolus has previously been impractical due to the lack of an efficient stable genetic transformation method. However, virus-induced gene silencing (VIGS) is effective in some plants which are difficult to transform through other methods. Although the Tobacco rattle virus (TRV)-based VIGS system has been developed and used for verifying gene functions in diverse plants, an appropriate TRV-VIGS approach for gladiolus has not been established yet. In this report we describe the first use of the TRV-VIGS system for gene silencing in gladiolus. Vacuum infiltration of cormels and young plants with the GhPDS-VIGS vector effectively down-regulated the PHYTOENE DESATURASE ortholog GhPDS gene and also resulted in various degrees of photobleaching in Gladiolus hybridus. The reduction in GhPDS expression was tested after TRV-based vector infection using real-time RT-PCR. In addition, the progress of TRV infection was detected by fluorescence visualization using a pTRV2: CP-GFP vector. In conclusion, the TRV-mediated VIGS described here will be an effective gene function analysis mechanism in gladiolus.

First report of chlorotic and necrotic disease caused by Tobacco rattle virus on Capsicum annuum in Japan

Severe chlorosis and necrosis were observed on Capsicum annuum in Ibaraki Prefecture, Japan. A virus strain was isolated and identified as Tobacco rattle virus (TRV) by rod-shaped viral particles observed with transmission electron microscopy and by sequence analysis with a reverse transcription-polymerase chain reaction using TRV-specific primers. The disease was reproduced by back-inoculation to green pepper seedlings and their subsequent transplant into field soil containing putative nematode vectors, Trichodorus and/or Paratrichodorus. Thus, we showed that TRV is responsible for this novel disease. This report is the first of TRV infection of C. annuum in Japan.

Sustainable disease control using weeds as indicators: Capsella bursa-pastoris and Tobacco Rattle Virus

Iannetta PPM, Begg GS, Valentine TA & Wishart J (2010). Sustainable disease control using weeds as indicators: Capsella bursa-pastoris and Tobacco Rattle Virus. Weed Research 50, 511–514. Summary Arable weeds are believed to sustain disease outbreaks of the potato crop pathogen Tobacco Rattle Virus (TRV), which is particularly well-known for the costly damage it may cause to potato tubers. We describe a TRV-specific TaqMan™ based molecular-diagnostic quantitative RT-PCR method which showed that ecotypes of the widespread and common weed Capsella bursa-pastoris (shepherd’s purse) are highly susceptible to TRV infection and may be suitable as indicator species of TRV presence in situ. Soils from two sites (S1 and S2), previously diagnosed as harbouring high levels of TRV, were the subjects of infection tests using C. bursa-pastoris and the susceptible model bait species Petunia x hybrida. TRV infection was only detected in all S1-soil, but in none of the plants grown in S2-soil. S1 soil had been treated annually with nematicide and herbicide, whilst continuing to cultivate TRV susceptible crops. S2 soil had been farmed for 5 years without the application of synthetic pesticides according to organic standards and had been sown with non-TRV susceptible crops in three out of the 5 years of the rotation. Our observations led us to question the current recommendations that: ‘Weed control is important. Organic practices and set-aside may facilitate the re-introduction of TRV and/or the increase the distribution of the virus within a field ’. We suggest that more effective and less environmentally damaging crop protection can be achieved using rotations that employ non-susceptible crops, in concert with management strategies that encourage crop-weed co-existence.

First Report of Tobacco rattle virus in Peony in Alaska.

Peonies (Paeonia sp.) are highly valued for their large showy flowers in home gardens and commercially in the cut flower industry. In 2007, scattered peony (Paeonia lactiflora 'Sarah Bernhardt') plants cultivated on small plots at the University of Alaska Experimental Station in Fairbanks displayed distinct leaf ringspot patterns. Symptoms were more severe during the cooler months of the growing season (June and September), with symptom remission in the intervening warmer months. Leaf samples from six symptomatic plants were collected in July and from 20 symptomatic plants in September and assayed for viruses. Leaf samples (1 g) were assayed with a general protocol for plant virus extraction and partial purification with differential centrifugation followed by protein detection on stained sodium dodecyl sulfate-polyacrylamide gel electrophoresis (1). No distinct proteins indicative of viral coat protein(s) were detected. Tomato spotted wilt virus (TSWV) and Tobacco rattle virus (TRV), known pathogens of peony, were then specifically targeted. Total RNA was extracted from each sample with an RNeasy Plant Mini kit (Qiagen Inc., Valencia, CA) and used as the template for reverse transcription (RT)-PCR with random primers. TSWV was not detected by RT-PCR with tospovirus group-specific primers (Agdia, Inc., Elkhart, IN). A nested set of primers designed from the TRV 16-kDa protein gene on RNA1 (4) amplified an ~600-bp fragment from one of the symptomatic plants. This DNA was directly sequenced (GenBank Accession No. FJ357572) and BLAST searches in GenBank revealed as much as 95% nucleotide (nt) identity with TRV accessions J04347 and X03685. Additional primer pairs specific for TRV (2) amplified overlapping fragments with expected sizes of ~818, ~515, and ~290 bp from the 29- and 16-kDa protein genes on the 3'-end of RNA1 that were directly sequenced. Assembly of these sequences in Sequencher 4.8 (Gene Codes Corp., Ann Arbor, MI) resulted in a 1,422-nt sequence (Accession No. FJ357571) and Clustal X analysis (3) showed 93 to 94% nt identity to TRV isolates, -ORY (AF034622), -PpK20 (AF314165), -Pp085 (AJ586803), and -SYM (D00155). Mechanical inoculation of partially purified virions from the confirmed TRV-infected peony plant to Nicotiana benthamiana gave no symptoms to occasional ringspots, faintly curled leaves, and chlorotic blotches on N. tabacum 'Samsun', and local lesions on Chenopodium amaranticolor. TRV infection of these hosts was confirmed by RT-PCR. With electron microscopy, rod-shaped particles similar to TRV with a distinct central canal characteristic of TRV were seen occasionally only from inoculated N. benthamiana. On the basis of the biological and molecular data, we have determined the virus in the peony to be an isolate of TRV, tentatively named TRV-Peony. TRV was confirmed in only one other peony based on a sequenced 290-nt PCR fragment with 95% identity with the sequence from the other TRV-infected peony. Lack of TRV detection in the other symptomatic peonies was possibly due to low viral concentrations and interfering plant substances. Documentation of TRV in peonies is especially important to help avoid distribution of virus-infected vegetative propagation material. To our knowledge, this is the first report of TRV in this host in Alaska, but also of this virus in Alaska.

Tobacco mosaic virus 126-kDa Protein Increases the Susceptibility of Nicotiana tabacum to Other Viruses and Its Dosage Affects Virus-Induced Gene Silencing

The Tobacco mosaic virus (TMV) 126-kDa protein is a suppressor of RNA silencing previously shown to delay the silencing of transgenes in Nicotiana tabacum and N. benthamiana. Here, we demonstrate that expression of a 126-kDa protein-green fluorescent protein (GFP) fusion (126-GFP) in N. tabacum increases susceptibility to a broad assortment of viruses, including Alfalfa mosaic virus, Brome mosaic virus, Tobacco rattle virus (TRV), and Potato virus X. Given its ability to enhance TRV infection in tobacco, we tested the effect of 126-GFP expression on TRV-mediated virus-induced gene silencing (VIGS) and demonstrate that this protein can enhance silencing phenotypes. To explain these results, we examined the poorly understood effect of suppressor dosage on the VIGS response and demonstrated that enhanced VIGS corresponds to the presence of low levels of suppressor protein. A mutant version of the 126-kDa protein, inhibited in its ability to suppress silencing, had a minimal effect on VIGS, suggesting that the suppressor activity of the 126-kDa protein is indeed responsible for the observed dosage effects. These findings illustrate the sensitivity of host plants to relatively small changes in suppressor dosage and have implications for those interested in enhancing silencing phenotypes in tobacco and other species through VIGS.

Resistance of transgenic tobacco plants incorporating the putative 57-kDa polymerase read-through gene of Tobacco rattle virus against rub-inoculated and nematode-transmitted virus

Nicotiana tabacum plants were transformed with the 57-kDa read-through domain of the replicase gene of Tobacco rattle virus (TRV) isolate SYM. From a total of six lines containing the viral transgene, four displayed various levels of resistance to TRV infection. Transgenic plants from line 81G were highly resistant to foliar rub-inoculation with the homologous isolate, or with isolates TRV-PpK20 and TRV-PLB, which are almost identical to TRV-SYM in RNA1 sequence. Moreover, 81G plants were moderately resistant to the serologically and genetically distinct, highly pathogenic isolate TRV-GR. Resistance characteristics of line 81G remained stable over six generations. No unambiguous correlation was established between number of transgene insertion loci and level of resistance. Transgene-specific mRNA was clearly detected in plants from susceptible lines but only at an early developmental stage in resistant plants, indicating the operation of a RNA silencing resistance mechanism. Following challenge using viruliferous vector nematodes carrying TRV-PpK20 or by rub inoculation of roots, 81G plants did not show any symptoms and virus was not detected in leaves. However, virus was detected in roots but without apparent effects on plant growth and often at low concentration. When challenged with nematodes carrying TRV-GR, symptoms in aerial parts of 81G plants were less severe and much delayed compared to non-transgenic plants, although younger plants showed less resistance than older ones. No difference was detected in transgene transcript accumulation between leaves and roots of 81G plants. This is the first work reporting a broad level of pathogen derived resistance against two geographically and genetically distinct TRV isolates transmitted directly by their nematode vectors and provides further insight into the expression of transgenic resistance against naturally transmitted soil-borne viruses.

Establishment of Tobacco Rattle Virus (TRV) in Weeds and Cuscuta

ABSTRACTIn the period of 2000–2004 the following 12 weed species were proved hosts to tobacco rattle virus (TRV): Amaranthus retroflexus L.—amaranth pigweed, Atriplex patula L.—orache, Chenopodium album L.—lambs-quarters, Cirsium arvense (L.) Scop.—creeping thistle, Convolvulus arvensis L.—bindweed, Datura stramonium L.—thornapple, Polygonum lapathifolium L.—pale smartweed, Raphanus raphanistrum L.—wild radish, Solanum nigrum L.—black dog grape, Sonchus arvensis L.—perennial sow thistle, Sorghum halepensis (L.) Pers.—Johnson-grass and Xanthium strumarium L.—broad cocklebur. The highest percentage of TRV infected plants was found among the species C. album, A. patula, S. halepensis and S. arvensis—69%, 68%, 67% and 57%, respectively. Positive samples, i.e. TRV carriers, were given by 73 of a total of 149 weed plants, which is 49%. Two production crops in Bulgaria were found infested with the parasite weed dodder, which is another reservoir of TRV infection. Unlike the above mentioned weeds, it possibly transmits the virus to sugar beet without nematode mediators of Trichodoridae family. Based on some morphological data (yellow-orange colored stems and fruit) we assumed this was Cuscuta campestris Yuncker. TRV was identified in self-seeded sugar beet, grown post-harvest on a field of wheat with predecessor sugar beet.

Tobacco Rattle Virus (TRV) Transmission by Sugar Beet Seeds

ABSTRACTThe study involves tobacco rattle virus (TRV) detection in racemes of two-year beet plants, seedlings, grown from seeds of these plants and seedlings from commercially available sugar beet seeds. Parts of sugar beet roots with a history of TRV were used for growing of two-year floriferous plants. Since plants had symptoms of yellow mosaic on leaves and raceme stipules, we tested each raceme separately with antiserum to TRV and broad beans wilt virus (BBWV) by ELISA. BBWV also causes yellow mosaic on leaves and raceme stipules and is usually combined with TRV infection in beet lately. Of 13 flowering plants, 8 were diagnosed with TRV and 2—with BBWV. TRV virus concentration in racemes was more than 0.3 to more than 0.5 optical units. BBWV showed lower concentration—more than 0.25 optical units in a limited number of plants (only 2), which did not interfere with TRV detection in racemes of flowering beet plants. Artificial vegetative propagation of beet has led to TRV transmission with racemes of two-year beet plants of up to 62%. Seedlings, originating from seeds of two-year beet plant, with extinction value of 0.550 optical units for the sample of its raceme, accounts for 20% of TRV transmission. The results of testing seedlings, grown from commercially available seeds, showed 15% TRV transmission for one batch and 20% for the other. TRV infection of racemes was investigated in samples, collected from a seed-production field. We detected 5% TRV infection in racemes of this field. The progeny of such racemes may transmit TRV to commercial fields, let alone nematode transmission of the virus.

Effects of systemic infections with Tobacco rattle virus on agronomic and quality traits of a range of potato cultivars

Infection of several commercially important potato cultivars with Tobacco rattle virus (TRV) can result in systemic infection with M‐type virus, which persists through generations of vegetative propagation, although spraing symptoms in the tubers rarely develop. In field trials of nine such cultivars it was shown that TRV infection can delay plant emergence and retard subsequent growth, reduce tuber yield and mean tuber weight, increase tuber numbers and the proportion of small tubers, increase the incidence of growth cracks and misshapen tubers, diminish dry matter content, and exacerbate after‐cooking blackening. Each cultivar was affected differently, showing different combinations and degrees of these effects. Virus concentration in leaf extracts from individual plants was also highly variable. These, and other potato cultivars similarly susceptible to TRV, are grown on large areas of UK and European potato land. The implications of growing such cultivars for the seed, ware and processing sectors of the potato industry are discussed.

Polypeptides induced by tobacco rattle virus during multiplication in tobacco protoplasts.

Tobacco protoplasts were irradiated with UV light, inoculated with tobacco rattle virus (TRV), and then cultured in media containing 35S-methionine. Polypeptides induced by TRV infection were detected by PAGE of protein extracts. Three 35S-labeled polypeptides (apparent molecular weights 187,000, 142,000, and 31,000) occurred in extracts of virus-infected protoplasts but not in extracts of buffer-inoculated protoplasts. The 31,000 mol. wt. polypeptides co-migrated with TRV coat protein in polyacrylamide gels and was not detected when inocula contained only the longer particle of TRV. The 187,000 and 142,000 mol. wt. polypeptides migrated in positions very close to products of in vitro translation of TRV RNA-1. Experiments in which 35S-methionine was supplied at different times during multiplication suggested that the bulk of translation of RNA-1 occurred sooner after inoculation than did that of RNA-2.