Cowpea Mosaic Virus-Encoded Protease Does Not Recognize Primary Translation Products of M RNAs from Other Comoviruses

The protease encoded by the large (B) RNA segment of cowpea mosaic virus was tested for its ability to recognize the in vitro translation products of the small (M) RNA segment from the comoviruses squash mosaic virus, red clover mottle virus, and cowpea severe mosaic virus (CPsMV, strains Dg and Ark), and from the nepovirus tomato black ring virus. Like M RNA from cowpea mosaic virus, the M RNAs from squash mosaic virus, red clover mottle virus, CPsMV-Dg, and CPsMV-Ark were all translated into two large polypeptides with apparent molecular weights which were different for each virus and even for the two CPsMV strains. Neither the in vitro products from squash mosaic virus, red clover mottle virus, and CPsMV M RNAs nor the in vitro product from tomato black ring virus RNA-2 were processed by the cowpea mosaic virus-encoded protease, indicating that the activity of this enzyme is highly specific.     

Resistance to six viruses in the legume goat's rue {Galega orientalis Lam.)

Plants from 2nd to 6th year leys of the legume goat's rue (Galega orientalis Lam.) were tested for infection with bean yellow mosaic (BYMV), bean common mosaic (BCMV), alfalfa mosaic (AMV), broad bean stain (BBSV), red clover mottle (RCMV) and cucumber mosaic (CMV) viruses by enzyme-linked immunosorbent assay (ELISA), electron microscopy, and by sap-inoculation to various test plant species. No virus infections were observed in goat's rue in the field. Glasshouse-grown seedlings of goat's rue were inoculated with the above viruses. No virus was detected in the inoculated plants. The results suggest that goat's rue is extremely resistant to the above six viruses which are important in other forage legumes.     

Comparative sequence and structure of viroid-like RNAs of two plant viruses.

A newly discovered group of spherical plant viruses contains a bipartite genome consisting of a single-strand linear RNA molecule (RNA 1, Mr 1.5 x 10(6) ), and a single-strand, covalently closed circular viroid-like RNA molecule (RNA 2, Mr approximately 125,000). The nucleotide sequences of the RNA 2 of two of these, velvet tobacco mottle virus and solanum nodiflorum mottle virus, have been determined. RNA 2 of solanum nodiflorum mottle virus consists of 377 residues whereas that of velvet tobacco mottle virus consists of two approximately equimolar species, one of 366 residues and the other, with a single nucleotide deletion, of 365 residues. There is 92-95% sequence homology between the RNA 2 species of the two viruses. The predicted secondary structures possess extensive intramolecular base pairing to give rod-like structures similar to those of viroids. The structural similarities between the RNAs 2 of velvet tobacco mottle virus and solanum nodiflorum mottle virus and viroids may reflect functional similarities.     

Characterization of a Tymovirus Isolated from Anagyris foetida as a Strain of Scrophularia Mottle Virus

A virus isolated from Anagyris foetida and infecting species in the Leguminosae and Solanaceae had typical properties of a tymovirus. It sedimented as two components (49 S and 103 S) and induced the formation of double membrane-bounded invaginations in the chloroplasts of infected cells. Large numbers of ‘empty shells’ were found in the nuclei. The coat protein had a molecular weight of c. 20.000 and the RNA consisted of c. 5500 nucleotides. Crystallization of the virus in laminal crystals could be achieved by precipitation with 10 % polyethylenglycol 6000 and 1 % NaCl. Serologically, the virus was closely related to Scrophularia mottle, Ononis yellow mosaic and Plantago mottle viruses. The four viruses which all infect leguminous hosts are separated by serological differentiation indices which are mostly between 1 and 3. It is therefore suggested that they all should be considered as strains of the same virus which for reasons of priority should have the name Scrophularia mottle virus (ScrMV). The proposed Anagyris strain clearly differs from the Scrophularia mottle, Ononis yellow mosaic and Plantago mottle strains of ScrMV in host range, symptomatology, electrophoretic mobility serological properties and some cytopathogenic effects. It is not clear why the Anagyris strain infects A. foetida systemically in nature, but only locally under greenhouse conditions.     

RED CLOVER MOTTLE VIRUS

A virus, provisionally named red clover mottle virus (RCMV), isolated from red clover plants in England, seems distinct from any previously described. It was transmitted by mechanical inoculation of sap to many legumes and to Gomphrena globosa L., but it was not transmitted by six aphid species, or through soil or through seeds.
RCMV is inactivated in 10 min. between 60 and 63°C., and in 8 days at 18°C., but survives for long periods at -20; sap was not infective when diluted more than 1/1000. The virus is soluble in the pH range (4–7) in which it is stable. It was precipitated without inactivation by 50% saturated ammonium sulphate solution, but it was inactivated by ethanol or acetone. Partially purified preparations contained polygonal particles about 28 mμ in diameter. Serological tests showed no antigens in common with broad bean mottle, true broad bean mosaic or lucerne mosaic viruses.     

Nucleotide sequence of Hungarian grapevine chrome mosaic nepovirus RNA1.

The nucleotide sequence of the RNA1 of hungarian grapevine chrome mosaic virus, a nepovirus very closely related to tomato black ring virus, has been determined from cDNA clones. It is 7212 nucleotides in length excluding the 3' terminal poly(A) tail and contains a large open reading frame extending from nucleotides 216 to 6971. The presumably encoded polyprotein is 2252 amino acids in length with a molecular weight of 250 kDa. The primary structure of the polyprotein was compared with that of other viral polyproteins, revealing the same general genetic organization as that of other picorna-like viruses (comoviruses, potyviruses and picornaviruses), except that an additional protein is suspected to occupy the N-terminus of the polyprotein.     

The r144 major histocompatibility complex class I-like gene of rat cytomegalovirus is dispensable for both acute and long-term infection in the immunocompromised host

The rat cytomegalovirus (RCMV) r144 gene encodes a polypeptide homologous to major histocompatibility complex class I heavy chains. To study the role of r144 in virus replication, an RCMV r144 null mutant strain (RCMVDeltar144) was generated. This strain replicated with efficiency similar to that of wild-type (WT) RCMV in vitro. Additionally, WT RCMV and RCMVDeltar144 were found not to differ in their replication characteristics in vivo. First, the survival rate was similar among groups of immunosuppressed rats infected with either RCMVDeltar144 or WT RCMV. Second, the dissemination of virus did not differ in either RCMVDeltar144- or WT RCMV-infected, immunosuppressed rats, either in the acute phase of infection or approximately 1 year after infection. These data indicate that the RCMV r144 gene is essential neither for virus replication in the acute phase of infection nor for long-term infection in immunocompromised rats. Interestingly, in a local infection model in which footpads of immunosuppressed rats were inoculated with virus, a significantly higher number of infiltrating macrophage cells as well as of CD8(+) T cells was observed in WT RCMV-infected paws than in RCMVDeltar144-infected paws. This suggests that r144 might function in the interaction with these leukocytes in vivo.     

Three-dimensional structure of baculovirus-expressed Norwalk virus capsids.

The three-dimensional structure of the baculovirus-expressed Norwalk virus capsid has been determined to a resolution of 2.2 nm using electron cryomicroscopy and computer image processing techniques. The empty capsid, 38.0 nm in diameter, exhibits T = 3 icosahedral symmetry and is composed of 90 dimers of the capsid protein. The striking features of the capsid structure are arch-like capsomeres, at the local and strict 2-fold axes, formed by dimers of the capsid protein and large hollows at the icosahedral 5- and 3-fold axes. Despite its distinctive architecture, the Norwalk virus capsid has several similarities with the structures of T = 3 single-stranded RNA (ssRNA) viruses. The structure of the protein subunit appears to be modular with three distinct domains: the distal globular domain (P2) that appears bilobed, a central stem domain (P1), and a lower shell domain (S). The distal domains of the 2-fold related subunits interact with each other to form the top of the arch. The lower domains of the adjacent subunits associate tightly to form a continuous shell between the radii of 11.0 and 15.0 nm. No significant mass density is observed below the radius of 11.0 mm. It is suspected that the hinge peptide in the adjoining region between the central domain and the shell domain may facilitate the subunits adapting to various quasi-equivalent environments. Architectural similarities between the Norwalk virus capsid and the other ssRNA viruses have suggested a possible domain organization along the primary sequence of the Norwalk virus capsid protein. It is suggested that the N-terminal 250 residues constitute the lower shell domain (S) with an eight-strand beta-barrel structure and that the C-terminal residues beyond 250 constitute the protruding (P1+P2) domains. A lack of an N-terminal basic region and the ability of the Norwalk virus capsid protein to form empty T = 3 shells suggest that the assembly pathway and the RNA packing mechanisms may be different from those proposed for tomato bushy stunt virus and southern bean mosaic virus but similar to that in tymoviruses and comoviruses.     

Nucleotide sequence of Chinese rape mosaic virus (oilseed rape mosaic virus), a crucifer tobamovirus infectious on Arabidopsis thaliana

The complete nucleotide sequence of Chinese rape mosaic virus has been determined. The virus is a member of the tobamovirus genus of plant virus and is able to infect Arabidopsis thaliana (L.) Heynh systemically. The analysis of the sequence shows a gene array that seems to be characteristic of crucifer tobamoviruses and which is slightly different from the one most frequently found in tobamoviruses. Based on gene organization and on comparisons of sequence homologies between members of the tobamoviruses, a clustering of crucifer tobamoviruses is proposed that groups the presently known crucifer tobamovirus into two viruses with two strains each. A name change of Chinese rape mosaic virus to oilseed rape mosaic virus is proposed.Abbreviations 2-ME 2-mercaptoethanol - EDTA ethylenediaminetetraacetic acid - SDS sodium dodecyl sulfate - UTR untranslated region - MP movement protein - CP capsid protein - CRMV Chinese rape mosaic virus - TVCV turnip vein clearing virus - PaMMV paprika mild mottle virus - PMMV-I pepper mild mottle virus (Italian isolate) - PMMV-S pepper mild mottle virus (Spanish isolate) - ToMV tomato mosaic virus - TMV tobacco mosaic virus - TMGMV tobacco mild green mosaic virus - ORSV odontoglossum ringspot virus - SHMV sunn hemp mosaic virus - CGMMV cucumber green mottle mosaic virus - ORMV oilseed rape mosaic virus     

THE PROPERTIES OF TOMATO ASPERMY VIRUS AND ITS RELATIONSHIP WITH CUCUMBER MOSAIC VIRUS*

Chrysanthemum plants infected with tomato aspermy virus (TAV) produce severely distorted and discoloured flowers but show only slight leaf mottle.
TAV infected twenty-five of forty-five species (belonging to seventeen genera) tested and was transmitted by the aphid species Aulacorthum solarti, Macrosiphoniella sanborni and Myzus persicae .
Sap from infected tobacco leaves lost infectivity when diluted more than 1 in 10,000, when heated for 10 min. at above 65°C. and when stored for more than 42 hr. at 16–18°C.
Partial protection was obtained between TAV and two strains of cucumber mosaic virus. Evidence was obtained that this was true protection between related viruses and serological tests confirmed the view that TAV is a strain of cucumber mosaic virus. Evidence was obtained that this was true protection between related viruses and serological tests confirmed the view that TAV is a strain of cucumber mosaic virus.     

The incidence of virus diseases in English sweet-cherry orchards and their effect on yield

Two thousand sweet-cherry trees (Prunus avium) in English orchards were tested for virus infection by using Lambert and Mazzard F 12/1 as indicators. Most trees of varieties commonly grown before 1920 were infected with more than one virus, usually little cherry (69%) and necrotic ringspot/prune dwarf (56%). Other infection was less prevalent, 35% of these trees having European rusty mottle, 30% ring mottle and 3% necrotic rusty mottle. Most trees of varieties introduced since 1920 were virus-free (61%) but some had become infected with each of these viruses except necrotic rusty mottle. In a field trial of 12 years duration the yield of three varieties was diminished by infection with necrotic ringspot/prune dwarf, rugose mosaic, rusty mottle, ring mottle and necrotic line pattern. The effect of rusty mottle was due to growth suppression resulting in smaller trees, but that of other viruses was also due to impaired fertility. The yield of one variety (Merton Heart) was greatly enhanced by infection with rugose mosaic, rusty mottle and necrotic ringspot/prune dwarf viruses. The high incidence of virus infection and consequent yield depression has probably diminished the potential yield by at least 30% and contributed to the decline in acreage of sweet cherries in England.     

Purification and properties of lucerne Australian symptomless virus, a new virus infecting lucerne in Australia

A virus with isometric particles c. 26–28 nm in diameter isolated from naturally infected lucerne (Medicago sativa) in Australia and reported there to be a strain of lucerne Australian latent virus (LALV), is shown to be a distinct virus. The virus, called lucerne Australian symptomless (LASV), was mechanically transmitted to 10 of 22 plant species inoculated, but only induced symptoms in three Chenopodium species and Gomphrena globosa. Virus particles occurred in relatively low concentrations in plant sap, and the virus could not be reliably maintained in culture by serial transmission to plants during winter (October-April). During the summer, sap of infected C. quinoa remained infective after diluting 10^-2 but not 10^-3, after heating for 10 min at 50 but not 55 ^oC and after storage for 24 days (the longest period tested) at 20, 4 and -15 ^oC. LASV was seed-borne to 6% of C. quinoa seedlings. Partially purified preparations of virus particles contained one nucleoprotein component with a sedimentation coefficient of c. BOS. Particles contained two polypeptide species of estimated mol. wts 26 000 and 40 000, and two ssRNA species which, when denatured in glyoxal, had apparent mol. wts of 2–5 times 10⁶ and 1–4 times 10⁶. The infectivity of virus RNA was abolished by incubation with proteinase K. Purified particles of LASV reacted with homologous antiserum (gel diffusion titre 1:256) but not with antiserum to LALV or to 13 other plant viruses with isometric particles including arracacha B (AVB), broad bean wilt, rubus Chinese seed-borne (RCSV) and strawberry latent ringspot (SLRV) viruses, and five comoviruses. These properties distinguish LASV from LALV and from all recognised nepoviruses and comoviruses. Its closest affinities are with SLRV, RCSV and possibly AVB; these viruses may comprise a distinct virus group or nepovirus subgroup.     

Immunodiagnosis of plant viruses by a virobacterial agglutination test

A new virobacterial agglutination (VBA) test for the immunodiagnosis of plant viruses is described. The test is based on the agglutination of Staphylococcus aureus cells by virus particles after treatment of the cells with homologous antiserum. The agglutination occurs within 1–5 min. The sensitivity of the test is 0·1-0·4 μg virus/ml and is not affected by the shape of the virus particle. The use of affinity purified antibodies for sensitisation of S. aureus cells increases the sensitivity of the reaction 50-fold and enables the detection of tobacco mosaic and cucumber green mottle mosaic viruses at a concentration of 2 ng/ml. The VBA test allows the estimation of potato viruses X, S, M and Y in the eyes and sprouts of infected tubers and in the leaves of infected plants. The diagnosis of carnation mottle virus in carnation plants and of mushroom viruses in mushroom (Agaricus bisporus) fruit-bodies and mycelium are also described.     

Viruses detected in Ullucus tuberosus (Basellaceae) from Peru and Bolivia

Ullucus tuberosus (Basellaceae) plants from 12 locations in the Andean highlands of Peru and Bolivia contained complexes of either three or four viruses. Specimens from six sites in Peru contained a potexvirus, a tobamovirus, a potyvirus and a comovirus, but those from another location lacked the potexvirus. All samples from five sites in Bolivia lacked the tobamovirus. The potexvirus (PMV/U) is a strain of papaya mosaic virus differing slightly from the type strain (PMV/T) in inducing milder symptoms in some common hosts and failing to infect a few other species. It symptomlessly infected U. tuberosus, and infected 15 of 29 species from seven of nine other families. PMV/U showed a close serological relationship to PMV/T and to boussingaultia mosaic virus and a distant relationship to commelina virus X, but it is apparently unrelated to any of ten other potexviruses. The tobamovirus (TMV/U) induced symptomless or inconspicuous infection in U. tuberosus, and infected 21 of 30 species from six of eight other families. It showed a very distant serological relationship to some strains of ribgrass mosaic, tobacco mosaic and tomato mosaic viruses, but failed to react with antisera to cucumber green mottle mosaic, frangipani mosaic, odontoglossum ringspot and sunn-hemp mosaic viruses. The potyvirus, tentatively designated ullucus mosaic virus (UMV), alone in U. tuberosus induced leaf symptoms indistinguishable from the chlorotic mottling and distortion found in naturally infected plants. UMV infected 12 of 20 species from four other families, and was transmitted in the non-persistent manner by Myzus persicae. It showed a distant serological relationship to only two (bidens mottle and alstroemeria mosaic) of 25 members or possible members of the potyvirus group tested. Some hosts and properties of the comovirus are described in an accompanying paper. None of the four viruses infected potato (Solanum tuberosum) and, with the possible exception of UMV, they differed from viruses reported previously to infect three other vegetatively propagated Andean crops (Oxalis tuberosa, Arracacia xanthorrhiza and Tropaeolum tuberosum).     

Glycine mosaic virus: a comovirus from Australian native Glycine species

Two strains of a virus designated Glycine mosaic virus (GMV) were found in Glycine clandestina and G. tabacina, legumes indigenous to Australia and the western Pacific region. When transmitted by sap inoculation, GMV infected mostly leguminous species, and caused mosaic and mottling symptoms. The virus was not found naturally in soybean G. max, but it infected all of the 21 cultivars tested. GMV has isometric particles of c. 28 nm diameter, and produces three components with sedimentation coefficients of 60 S (top), 103 S (middle), and 130 S (bottom). Both middle and bottom components are required for infectivity. The virions contain two major proteins with molecular weights of c. 21 500 and 42 000. GMV produces large aggregates of particles in the cytoplasm of the mesophyll cells of pea Pisum sativum, and also induces amorphous membrane-bound bodies and cytoplasmic vesicles. The type strain (from New South Wales) reacts with antisera to Echtes Ackerbohnenmosaik, broad bean stain, and a Californian isolate of squash mosaic virus. The GW strain (from Queensland) reacts with all of the latter antisera, as well as with antisera to cowpea mosaic virus (Sb and Ark strains), bean pod mottle, and red clover mottle viruses, and is serologically related to, but not identical with, the type strain. These properties clearly establish GMV as a new member of the comovirus group.     

Lamium mild mosaic virus: a virus distantly related to broad bean wilt

Lamium mild mosaic virus (LMMV) was compared with some strains of broad bean wilt virus (BBWV). It differed somewhat in host range from BBWV; serologically, it was only distantly related to four strains of BBWV, all belonging to serotype I, but no reaction was detected with serotype II. BBWV and LMMV were not serologically related to six comoviruses. Like BBWV, LMMV sedimented in three components and the two viruses were morphologically indistinguishable, but LMMV had more slowly migrating RNAs and coat proteins. No distinctive pathological changes were seen in LMMV infected cells. It is proposed that LMMV be considered a distinct virus from BBWV but included with it in a new group of plant viruses.     

Homologous sequences in non-structural proteins from cowpea mosaic virus and picornaviruses

Computer analyses have revealed sequence homology between two non-structural proteins encoded by cowpea mosaic virus (CPMV), and corresponding proteins encoded by two picornaviruses, poliovirus and foot-and-mouth disease virus. A region of 535 amino acids in the 87-K polypeptide from CPMV was found to be homologous to the RNA-dependent RNA polymerases from both picornaviruses, the best matches being found where the picornaviral proteins most resemble each other. Additionally, the 58-K polypeptide from CPMV and polypeptide P2-X from poliovirus contain a conserved region of 143 amino acids. Based on the homology observed, a genetic map of the CPMV genome has been constructed in which the 87-K polypeptide represents the core polymerase domain of the CPMV replicase. These results have implications for the evolution of RNA viruses, and mechanisms are discussed which may explain the existence of homology between picornaviruses (animal viruses with single genomic RNAs) and comoviruses (plant viruses with two genomic RNAs).     

Broad-bean stain and true broad-bean mosaic viruses

Autumn-sown crops of broad beans (Vicia faba L.) in England often contain plants with some leaves characteristically distorted and with a chlorotic mosaic. From some of these plants true broad-bean mosaic virus was isolated in 1959 and 1960 but not in 1965 and 1966. From other plants a similar but distinct virus, which caused staining of the seeds and we call broad-bean stain virus, was isolated in 1960, 1965 and 1966. The two viruses were readily distinguished in serological tests, and in some test plants. Both were seed-borne, and spread in crops, but were not transmitted by several animal species tested as vectors. Both viruses have isometric particles about 25 mμ in diameter. Some of these particles contain about 35% ribonucleic acid, some about 26% and some of those of broad-bean stain virus contain none; these three types of particles had sedimentation coefficients of about 120–130 S, 100 S and 60 S respectively. The ribonucleic acid of each virus had molar base content of G 23%, A 26%, C 18% and U 32%. These two viruses are members of the cowpea mosaic group of plant viruses; broad-bean strain virus was serologically related to cowpea mosaic, F I, red-clover mottle, and squash mosaic viruses. The particles of all these viruses and of true broad-bean mosaic virus were similar in appearance, sedimentation behaviour, and nucleic acid content and composition. The nucleic acid of red-clover mottle virus had a molar base content of G 20%, A 29%, C 20%, U 30%.     

Investigation of Ukrainian isolates of cucumber green mottle mosaic virus

Abstract

Isolates of cucumber green mottle mosaic virus (CGMMV) obtained from three greenhouses in Ukraine have been identified. The rabbit antisera have been generated for these isolates. These antisera can be used for diagnostics of CGMMV in plant material by indirect ELISA. Analysis of cDNA sequences of capsid protein of these viruses confirmed that they may be grouped into novel strain of CGMMV.