The behaviour of some naturally occurring strains of potato virus Y

Potato virus Y was obtained from field crops of potatoes in many strains which differed widely in virulence and caused diseases in the variety Majestic ranging from severe leaf-drop streak to mild mosaic. The symptoms caused by these strains in seven potato varieties and tobacco are described and compared with those caused by the serologically related potato virus C. No changes were noted in the behaviour of any of the strains over three years, during which they were transmitted to many different plants.
Potato virus C was not transmitted by Myzus persicae , the most efficient vector of other strains of virus Y. Nor was virus C transmitted by eleven other species of aphides, eight of which transmitted virus Y. The efficiency with which different species acted as vectors of virus Y varied greatly, and it is suggested that in some species only occasional individuals can transmit.
Possible mechanisms for the evolution of viruses C and Y are indicated, and the effects of changes in virus, vector, and host on the prevalence of insect-transmitted viruses are discussed.     

Preliminary survey of potato virus Y (PVy) strains in potato samples from Kurdistan (Iran)

Potato virus Y (PVY) is the type species in the potyvirus genus of the family potyviridae. This plant pathogenic virus is transmitted through plant sap inoculation by stem and core grafting and by at least 25 aphid species in a non-persistent manner. According to potato specialists in most parts of the world, PVY is currently considered as the most harmful virus in cultivated potatoes. This is also the case for potato production in Iran. In this project we investigated potato leaves that were collected in the Kurdistan province in Iran for the presence of PVY with use of different biochemical/molecular techniques as ELISA, RT-PCR and qPCR. The different PVY strains, including PVY-O, PVY-N, PVYN-TN, PVY-NWi, were determined by using a triplex RT-PCR. In conclusion, the results demonstrated the presence of PVY-NWi strains in the potato leaf samples from Kurdistan (Iran). The data are discussed in relation to prevalence of PVY strains in Iran.     

Resistance to potato virus Y and potato virus X in Solanurn brevidens

Although Solanum brevidens could be infected with potato virus X (PVX), potato virus Y⁰ (PVY⁰) and PVY^N, no symptoms of infection were apparent and tests by double antibody sandwich ELISA, electron microscopy and sap transmission to local lesion test plants indicated that the titres of PVX were less than a tenth of those of PVY⁰ and PVY^N were less than a hundredth of those in infected plants of PDH40, a susceptible dihaploid clone of S. tuberosum cv. Pentland Crown. Furthermore, PVY⁰- and PVY^N- infected leaves of S. brevidens were a poor source of inoculum in aphid transmission tests. The possibility of a common mechanism and genetic basis of resistance to PVY, PVX and potato leaf roll virus in S. brevidens is discussed.     

Ultrastructural events during hypersensitive response of potato cv. Rywal infected with necrotic strains of potato virus Y

Potato plants cv. Rywal with hypersensitivity gene Ny-1 infected with PVY^N or PVY^NTN reacted in local necroses 3 days after infection. Potato virus Y (PVY) particles were found in epidermis, mesophyll, phloem and xylem cells in inoculated leaves. Noncapsidated virus particles (without capsid protein) were observed already 10 h after infection by using electron microscopy in situ. Capsid protein on one terminus of noncapsidated virus particles was located 5 days after inoculation with the use of immunogold labeling method. Whereas cytoplasmic inclusions were observed for the first time 24 days after infection during hypersensitive response. Ultrastructural studies showed that ER may take part in PVY RNA replication and capsidation of Potyvirus particles. Observed cytopathological changes and virus particles indicate that cell nucleus and mitochondrion might participate in PVY life cycle. During hypersensitive response PVY particles were found in plasmodesmata as well as in phloem and xylem.     

Molecular mapping of the potato virus Y resistance gene Rysto in potato

Ry _sto is a dominant gene which confers resistance to potato virus Y (PVY) in potato. We have used bulked segregant analysis of an F₁ tetraploid potato population to identify three AFLP markers linked to and on either side of Ry _sto . The tomato homologue of one of these AFLP markers was assigned to linkage group XI by analysis of an F₂ mapping population of tomato, suggesting that Ry _sto is also on chromosome XI of the potato genome. This map position was confirmed by the demonstration that Ry _sto was linked to markers which had been previously mapped to chromosome XI of the potato genome. Four additional AFLP markers were identified that were closely linked to Ry _sto in a population of 360 segregating progeny of a potato cross between a resistant (Ry _sto ) and a susceptible parent. Two of these markers were on either side of Ry _sto , separated by only a single recombination event. The other two markers co-segregated with Ry _sto . Received: 29 July 1996 / Accepted: 30 August 1996     

A model for the hepatitis B virus core protein: prediction of antigenic sites and relationship to RNA virus capsid proteins.

The sequences of the core proteins from several serotypes of human hepatitis B virus and related mammalian and avian hepadnaviruses are aligned with the vp3 capsid protein of mengo virus, a picornavirus. The homology indicates an eight-stranded antiparallel beta-barrel fold for the hepatitis protein, as observed in the tertiary structure of the picornavirus protein. The locations of known antigenic sites and other modifications are consistent with this structure for the core protein. The predicted folding suggests additional exposed antigenic sites and supports an evolutionary relationship between this family of enveloped DNA viruses and enveloped and non-enveloped RNA viruses.     

Crop borders reduce potato virus Y incidence in seed potato

Crop borders of soybean (Glycine max), sorghum (Sorghum bicolor), winter wheat (Triticum aestivum) and potato (Solanum tuberosum) were tested as a means of reducing potato virus Y (PVY) incidence in seed potato. Borders of fallow cultivated ground served as controls. Aphid landing rates were monitored weekly in plots using green tile traps, and PVY incidence was assessed by serologically testing tuber progeny from selected rows in each plot. Average weekly aphid landing rates in fallow-bordered and crop-bordered plots were not significantly different in 1992 (29.4 and 25.2 aphids, respectively) or 1993 (7.3 and 6.6 aphids, respectively). However, crop borders significantly reduced PVY incidence. In 1992, fallow-bordered and soybean-bordered plots averaged 47.8% and 35.0% PVY infection, respectively. In 1993, PVY infection averaged across all crop (soybean, sorghum, and wheat) bordered plots was 2.7% compared to 6.8% in fallow-bordered plots. PVY incidence in the centre rows of fallow-bordered and crop-bordered plots was statistically equivalent, while outer rows of crop-bordered plots had significantly less PVY than outer rows of fallow-bordered plots. Crop borders apparently reduced the number of viruliferous aphids landing on the edge of the plot. The choice of crop species used as a border, or treating the border with a systemic insecticide, did not affect aphid landing rates or PVY incidence. In 1995, PVY incidence in the centre 10 row block of potatoes averaged 2.1% across all crop borders (potato and soybean). PVY infection in the four row potato border averaged 5.7%. Crop borders are readily adaptable to current production practices, although the greatest benefits in reducing PVY incidence would occur in average sized, generation 0 (< 0.2 ha), elite seed potato fields.     

Molecular interactions of Epstein-Barr virus capsid proteins

The capsids of herpesviruses, which comprise major and minor capsid proteins, have a common icosahedral structure with 162 capsomers. An electron microscopic study shows that Epstein-Barr virus (EBV) capsids in the nucleus are immunolabeled by anti-BDLF1 and anti-BORF1 antibodies, indicating that BDLF1 and BORF1 are the minor capsid proteins of EBV. Cross-linking and electrophoresis studies of purified BDLF1 and BORF1 revealed that these two proteins form a triplex that is similar to that formed by the minor capsid proteins, VP19C and VP23, of herpes simplex virus type 1 (HSV-1). Although the interaction between VP23, a homolog of BDLF1, and the major capsid protein VP5 could not be verified biochemically in earlier studies, the interaction between BDLF1 and the EBV major capsid protein, viral capsid antigen (VCA), can be confirmed by glutathione S-transferase (GST) pulldown assay and coimmunoprecipitation. Additionally, in HSV-1, VP5 interacts with only the middle region of VP19C; in EBV, VCA interacts with both the N-terminal and middle regions of BORF1, a homolog of VP19C, revealing that the proteins in the EBV triplex interact with the major capsid protein differently from those in HSV-1. A GST pulldown study also identifies the oligomerization domains in VCA and the dimerization domain in BDLF1. The results presented herein reveal how the EBV capsid proteins interact and thereby improve our understanding of the capsid structure of the virus.     

Synthesis and immunochemical properties of oligopeptides--fragments of capsid proteins of the hepatitis A virus]

The hepatitis A virus (HAV) capsid protein VP1, VP2 and VP3 are exposed at the virion surface and should therefore contain antigenic determinants. Algorithms for hydrophilicity, antigenicity and flexibility were used to predict probable antigenic sites. Synthesis of 7- to 23-membered overlapping peptides from seven sites, viz., 1-11, 1-17, 2-33, 11-25, 73-82, 76-86, 98-109, 98-112, 102-107, 102-108, 108-127, 113-123, 118-140, 276-298 from VP1, 42-62 from VP2, 76-85 from VP3, and 1-23 from VP4, was performed by various solid-phase methods. Free peptides and their conjugates with different carriers were used for immunization and study of antigenicity. The peptides did not interact with antibodies to the hepatitis A virus, whereas their conjugates did not induce the formation of anti-HAV-antibodies.     

Probable epitopes of adenovirus capsid proteins]

The hydrophilicity and flexibility patterns of two capsid proteins of type 2 human adenovirus (hexon and fiber) were obtained. Several sites with maximal hydrophilicity and flexibility were revealed; their correlation was partly established. The role of these sites in the formation of adenoviral capsid protein epitopes is discussed.     

Biological and molecular characterization of two tomato strains of potato virus Y (PVY)

Two PVY tomato strains (LYE 84 and LYE 84.2), arising from the same natural isolate, and a strain originating from a wild Solanaceous host, Solanum nigrum (SON 41.2), were compared for host range and symptomatology. All strains induced mosaic without necrosis on tobacco as PVY^O strains. The two tomato strains behaved similarly on pepper, infecting only susceptible pepper cultivars (pathotype 0), whereas SON 41.2 was able to overcome the two alleles of the recessive resistance gene pvr2 (pathotype 1.2). On the other hand, only LYE 84.2 was virulent on tomato and broke the resistance of the wild genitor Lycopersicon hirsutum PI 247087. Sequence determination of the capsid gene and the 3′ non-coding region of LYE 84 and LYE 84.2 showed a total homology at both nucleic acid and amino acid levels. This suggests that LYE 84.2 has probably derived from LYE 84, that both strains have very similar sequences and that the capsid protein does not play a direct role in the resistance-breaking capacity of LYE 84.2.     

Simian virus 40 chromatin interaction with the capsid proteins

It has been established that both in virions and in infected cells, the cellular core histones fold the SV40 DNA into nucleosomes to form the SV40 chromosome or chromatin. We and others have begun to examine how the capsid proteins assemble the SV40 chromatin into virions and to investigate whether these proteins interact with the encapsidated chromatin. To follow the pathway of virus assembly, we have analyzed the nucleoproteins which accumulate in cells infected with the SV40 mutants temperature-sensitive in assembly: tsC, tsBC, and tsB. (The temperature-sensitivity of these mutants result from alterations in the amino acid sequence of the major capsid protein VP1). We have found that mutants belonging to the same class accumulate similar types of nucleoproteins at the nonpermissive temperature (40 degrees C) and thus, share characteristics in common. For example, the tsC mutants accumulate only the 75 S chromatin. Both tsBC and tsB mutants produce in addition to chromatin, nucleoprotein complexes which sediment broadly from 100-160 S and contain all the three capsid proteins VP1, VP2, and VP3. These nucleoproteins can be distinguished morphologically, however. Under the electron microscope, the tsBC 100-160 S nucleoproteins appear as chromatin to which a small cluster of the capsid proteins is attached; the tsB nucleoproteins appear as partially assembled virions. In addition, we find that the 220 S virions are assembled in cells coinfected with tsB and tsC mutants at 40 degrees C, in agreement with genetic analysis. Our observations favor the hypothesis that the VP1 protein contains three discrete domains. We speculate that each domain may play a specific function in SV40 assembly. To gain more insight into VP1-VP1 interactions, we have examined the nucleoproteins which result from treatment of the mature wild-type virions with increasing concentrations of the reducing agent DTT. In the presence of as low a concentration of DTT as 0.1 mM, the virion shell can be penetrated by micrococcal nuclease, which then cleaves the viral DNA. This result indicates that some of the disulfide bonds bridging the VP1 proteins are on the virion surface.     

Comparison of antigenic properties of the X-potato virus and its coat proteins. Effect of proteolytic cleavage on antigenic characteristics

Antigenic properties of intact potato virus X (PVX) particles and of PVX coat protein (CP) preparations were compared using different modifications of ELISA test. In the competitive ELISA test (reaction in solution) antibodies to intact virus react much stronger with PVX than with CP while antibodies to CP react much stronger with CP than with PVX. In the direct ELISA test (reaction on the solid support) the difference in reactions of antiCP antibodies with PVX and CP is eliminated while the one in reactions of antiPVX antibodies with these antigens remains. No difference was registered in reactivity of PVX absorbed directly on polystyrene or on immunoglobulin-coated wells (sandwich ELISA) to antiCP antibodies.     

Varietal differences in susceptibility to potato virus Y

In addition to giving different kinds of symptoms when infected with potato virus Y , individual potato varieties also differ in their susceptibility to infection, in the concentration of virus attained in their sap, and in their efficiency as sources of virus for aphides. Their relative susceptibility in the open when exposed to equal chances of infection is correlated with the ease with which they become infected when colonized with infective aphides, and can be assessed from tests made under glass. Methods for making such tests are described; these need few tubers and give reproducible results. It is considered that they could be applied in studying the inheritance of this type of resistance and to test the behaviour of new seedlings. The American variety Katahdin was the most resistant of those tested, but there were significant differences between commercial British varieties.
In the open, all varieties were equally colonized by aphides and resistance to infection with virus Y was not correlated with resistance to leaf roll.     

Adeno-associated virus proteins: origin of the capsid components.

The three primary capsid proteins (A, B, and C) of adeno-associated viruses have been shown previously to contain overlapping amino acid sequences (R. McPherson and J. Rose, J. Virol. 46:523-529, 1983). In the present study we demonstrate definitively that these proteins are encoded in the right half of the adeno-associated virus 2 genome, and one or both of the smallest adeno-associated RNA species (2.3- or 2.6-kilobase RNA) account for their synthesis. Protein A (90 kilodaltons) apparently initiates from a site within the intervening sequence, which is intact in the larger (unspliced) 2.6-kilobase mRNA, and may read through one or more termination codons, including a strong stop signal (UAA) that lies 31 bases downstream from the end of the intervening sequence. Proteins B (72 kilodaltons) and C (60 kilodaltons) are not derived from protein A but apparently originate from independent, in-frame initiations that lie downstream from the splice junction. It thus seems likely that production of the three adeno-associated virus capsid proteins involves at least two mRNA species. The B and C proteins presumably arise from the spliced 2.3-kilobase RNA, whereas protein A should be generated by the 2.6-kilobase RNA or a hitherto unidentified spliced RNA species.     

Immunochemical analysis of the synthetic peptides incorporated into the protein antigenic determinant of the potato virus X coat]

Three peptides located in the N-terminal region of the potato virus X coat protein were synthesized by hand solid phase method for epitope mapping of this protein. One of these peptides (nanopeptide) interacted with monoclonal antibodies to native virus X. On the basis of these studies it was assumed, that amino acid sequence of the potato virus X coat protein, which included lysine residue in position 19, is located on the virion surface.     

The antigenic characteristics of field strains of the rabies virus from different districts of the USSR studied using antinucleocapsid monoclonal antibodies

98 rabies virus strains isolated from different species of wild and domestic animals have been studied by means of 36 monoclonal antibodies obtained from the Wistar Institute (USA) and 3--of the Federal Research Center on Viral Diseases of Animals (FRG). The antigenic variants determined in this study have been analyzed in comparison with the data obtained in other regions of the world, thus establishing the spread of these variants and their relationship with different species of animals.