Evolutionary relationship of alfalfa mosaic virus with cucumber mosaic virus and brome mosaic virus

The amino acid sequences of the non-structural protein (molecular weight 35,000; 3a protein) from three plant viruses — cucumber mosaic, brome mosaic and alfalfa mosaic have been systematically compared using the partial genomic sequences for these three viruses already available. The 3a protein of cucumber mosaic virus has an amino acid sequence homology of 33.7% with the corresponding protein of brome mosaic virus. A similar protein from alfalfa mosaic virus has a homology of 18.2% and 14.2% with the protein from brome mosaic virus and cucumber mosaic virus, respectively. These results suggest that the three plant viruses are evolutionarily related, although, the evolutionary distance between alfalfa mosaic virus and cucumber mosaic virus or brome mosaic virus is much larger than the corresponding distance between the latter two viruses.     

Narcissus mosaic virus

Narcissus mosaic virus (NMV) is widespread in British crops of trumpet, large-cupped and double daffodils, but was not found in Narcissus jonquilla or N. tazzeta. Many commercial daffodil cultivars seem totally infected, and roguing or selection is therefore impracticable. Strict precautions by breeders and raisers to prevent infection of new cultivars is recommended. Healthy daffodil seedlings were readily infected with NMV by mechanical inoculation, but the virus was not detected in them until 17 months after inoculation, when a mild mosaic appeared. NMV infected twenty-eight of fifty-three inoculated plant species; only five (Nicotiana clevelandii, Gomphrena globosa, Medicago sativa, Trifolium campestre and T. incarnatum) were infected systemically, and NMV was cultured in these and assayed in Chenopodium amaranticolor and Tetragonia expansa. The virus was not transmitted to and from G. globosa or N. clevelandii by three aphid species, or through the seeds of Narcissus, G. globosa and N. clevelandii but was transmitted by handling. G. globosa sap was infective at a dilution of 10 ^-5 but not at 10^-6, when heated for 10 min. at 70° C. but not at 75° C, and after 12 weeks at 18° C, or 36 weeks at 0–4° C. NMV withstood freezing in infected leaves and sap, and purified preparations and freeze-dried sap remained infective for over 2 years. NMV was precipitated without inactivation by ammonium sulphate (313 g./l.) but was better purified by differential centrifugation of phosphate-buffer extracts treated with n-butanol. Such virus preparations from G. globosa, N. clevelandii, C. amaranticolor and T. expansa were highly infective, serologically active, produced a specific light-scattering zone when centrifuged in density-gradients and contained numerous unaggregated particles with a commonest length of 548–568 mμ. Antisera prepared in rabbits had precipitin tube titres of 1/4096. NMV was detected in three experimental hosts but not in narcissus sap. Unlike some viruses with elongated particles, NMV precipitates with antiserum in agar-gel. Purified preparations reacted with antiserum to a Dutch isolate of NMV but not with antisera to seven other viruses having similar particles and in vitro properties, or to narcissus yellow stripe virus.     

Interaction of cucumber mosaic virus and potato virus y with tobacco mosaic virus

A study was performed on the interaction of cucumber mosaic virus (CMV) of potato virus Y (PVY) with tobacco mosaic virus (TMV). Interference was evaluated using tobacco plantsNicotiana tabacum cv. Java responding to CMV and PVY with a systemic infection and to TMV with local necrotic lesions. The decrease in TMV — induced lesion number gave evidence of a decrease in susceptibility caused by the previous infection with CMV or PVY, the decrease of lesion enlargement demonstrated a decreased TMV reproduction in the plants previously infected with CMV or PVY. The interference concerned was incomplete, as evaluated from reproduction of the challenging TMV and from the decrease in susceptibility of the host to TMV brought about by the first infection with CMV or PVY.     

Comparison of the nucleotide sequences of cucumber mosaic virus and brome mosaic virus

Cucumber mosaic virus (CMV) and brome mosaic virus (BMV) are isometric plant viruses. Although biologically distinct, they share many common chemical properties. An analysis of the partial genomic RNA sequence available for these two viruses reveals that they are evolutionarily related. Different segments of the genome exhibit different evolutionary rates. The coat proteins, which serve as carriers of genetic material, possess little or no homology. In contrast, the 3a proteins show over 35% homology. The non-coding regions of the genome also exhibit extensive but variable homology suggesting the functional importance of the nucleic acid.     

Mild mosaic of spiraea caused by cucumber mosaic virus

A disease of spiraea(Spiraea xvanhouttei) manifested in leaves by very mild, mostly hardly perceptible mosaic, was found to be caused by cucumber mosaic virus (CMV) infection. The proof was given on the basis of responce of differential plants after virus transmission, by immunosorbent electron microscopy and ELISA.     

Inheritance of resistance to zucchini yellow mosaic virus and watermelon mosaic virus in watermelon

High resistance to zucchini yellow mosaic virus-China strain (ZYMV-CH) and moderate resistance to watermelon mosaic virus (WMV) were found in a selection of PI 595203 (Citrullus lanatus var. lanatus), an Egusi type originally collected in Nigeria. Mixed inoculations showed primarily that these two viruses have no cross-protection. This fact may explain the high frequency of mixed infection often observed in commercial fields. When plants were inoculated with a mixture of the two viruses, the frequency of plants resistant to ZYMV was lower than expected, indicating that WMV infection may reduce the ability of a plant to resist ZYMV. We studied inheritance of resistance to ZYMV-CH and WMV, using crosses between a single-plant selection of PI 595203 and the ZYMV-susceptible watermelon inbreds 9811 and 98R. According to virus ratings of the susceptible parents, the resistant parent, and the F1, F2, and BC1 generations, resistance to ZYMV-CH was conferred by a single recessive gene, for which the symbol zym-CH is suggested. The high tolerance to WMV was controlled by at least two recessive genes.     

Sequence analysis of a soilborne wheat mosaic virus isolate from Italy shows that it is the same virus asEuropean wheat mosaic virus andSoilborne rye mosaic virus

The complete sequence of the two RNAs of a furovirus isolate from durum wheat in Italy was determined. Sequence comparisons and phylogenetic analysis were done to compare the Italian virus withSoilborne wheat mosaic virus (SBWMV) from the USA and with furovirus sequences recently published asEuropean wheat mosaic virus (EWMV), from wheat in France, andSoilborne rye mosaic virus (SBRMV), from rye and wheat in Germany. Over the entire genome, the Italian isolate RNA1 and RNA2 had respectively 97.5% and 98.6% nucleotide identity with EWMV, 95.5% and 85.8% with SBRMV-G and 70.6% and 64.5% with SBWMV. The Italian isolate was therefore clearly distinct from SBWMV The European isolates all appear to belong to the same virus and the nameSoilborne cereal mosaic virus may resolve earlier ambiguities.     

Mutagenesis of cauliflower mosaic virus

A series of insertion mutants of cauliflower mosaic virus (CaMV) DNA has been constructed in vitro. These insertions consist of a short DNA sequence (10 or 22 bp) containing a restriction endonuclease site (SmaI) not represented on the viral DNA. Viral infectivity was analyzed by inoculating plants with the mutated cloned viral DNA and observing symptoms. Insertions within ORFVII, and in one site within the large intergenic region, did not interfere with viral infectivity, whilst insertions within ORFII and at the end of ORFIV retarded the development of viral symptoms. All other insertion mutants analyzed were lethal. CaMV with a deletion of 105 bp within ORFVII was viable. Such viable mutants can be used to construct additional deletions or to insert foreign DNA into the viral genome.     

Reassembly of brome mosaic virus from dissociated virus

The reconstitution of Brome Mosaic Virus (BMV) has been studied using neutron scattering. Experiments were performed on disassembled virus without subsequent separation of components. Phase diagrams of the disassembly and subsequent reassembly of BMV were established as a function of pH and LiCl molarity by analytical centrifugation and quasi-elastic light scattering. Disassembly occurs at a pH above 6.5 and above 0.8 M LiCl. On reassembly, if the pH is lowered first, capsids are formed without subsequent incorporation of RNA. Neutron scattering was used to investigate the formation of virus particles, when the ionic strength was lowered from 1.4 to 0.1 M LiCl at pH 7.8. The reconstitution was followed continuously. As it was driven by a lowering of the ionic strength the kinetics of the process cannot be studied for short times. However the fact that at any given ionic strength no evolution of the scattering was observed with time implies that the reconstitution is complete within a few minutes. The observations in buffers with various amounts of D₂O lead to the conclusion that the reassembly is achieved by co-condensation of the RNA and of the capsid proteins.     

Interaction of tobacco mosaic virus and tobacco mosaic virus protein with bovine serum albumin.

Bovine serum albumin (BSA) causes tobacco mosaic virus (TMV) to crystallize at pH values where both have negative charges. The amount of albumin required to precipitate the virus varies inversely with ionic strength of added electrolyte. At pH values above 5, the precipitating power is greatest when BSA has the maximum total, positive plus negative, charge. Unlike early stages of the crystallization of TMV in ammonium sulfate-phosphate solutions, which can be reversed by lowering the temperature, the precipitation of TMV by BSA is not readily reversed by changes in temperature. The logarithm of the apparent solubility of TMV in BSA solutions, at constant ionic strength of added electrolyte, decreases linearly with increasing BSA concentration. This result and the correlation of precipitating power with total BSA charge suggest that BSA acts in the manner of a salting-out agent. The effect of BSA on the reversible entropy-driven polymerization of TMV protein (TMVP) depends on BSA concentration, pH, and ionic strength. In general, BSA promotes TMVP polymerization, and this effect increases with increasing BSA concentrations. The effect is larger at pH 6.5 than at pH 6. Even though increasing ionic strength promotes polymerization of TMVP in absence of BSA, the effect of increasing ionic strength from 0.08 to 0.18 at pH 6.5 decreases the polymerization-promoting effect of BSA. Likewise, the presence of BSA decreases the polymerization-promoting effect of ionic strength. The polymerization-promoting effect of BSA can be interpreted in terms of a process akin to salting-out. The mutual suppression of the polymerization-promoting effects of BSA and of electrolytes by each other can be partially explained in terms of salting-in of BSA.     

Sequence analysis of a soil-borne wheat mosaic virus isolate from Italy shows that it is the same virus as European wheat mosaic virus and Soil-borne rye mosaic virus

The complete sequence of the two RNAs of a furovirus isolate from durum wheat in Italy was determined. Sequence comparisons and phylogenetic analysis were done to compare the Italian virus with Soil-borne wheat mosaic virus (SBWMV) from the USA and with furovirus sequences recently published as European wheat mosaic virus (EWMV), from wheat in France, and Soil-borne rye mosaic virus (SBRMV), from rye and wheat in Germany. Over the entire genome, the Italian isolate RNA1 and RNA2 had respectively 97.5% and 98.6% nucleotide identity with EWMV, 95.5% and 85.8% with SBRMV-G and 70.6% and 64.5% with SBWMV. The Italian isolate was therefore clearly distinct from SBWMV. The European isolates all appear to belong to the same virus and the name Soil-borne cereal mosaic virus may resolve earlier ambiguities.