Translational Cross-Activation of the Encapsidated RNA of Potexviruses

We had shown the genomic RNA of potexviruses potato virus X and the alternanthera mosaic virus to be inaccessible in vitro to ribosomes while in intact virion form, but the RNAs can be translationally activated following the binding of movement protein 1 (MP1) to virus particles. Here, we present the results of the follow-up study targeting two more potexvirus species - the Narcissus mosaic virus and the Potato aucuba mosaic virus. We found encapsidated potexviral RNA to share common translational features in vitro and the MP1 to be potent over homological virions of its own species and over heterological virions of other species, as well exhibiting selective specificity. Reciprocal cross-activation is observed among viral species phylogenetically either close or distant. There is direct evidence that MP1 binding to the end of the virion is necessary, but not sufficient, for translational activation of encapsidated RNA.

PRESERVATION OF ANTIGEN PREPARATIONS FOR PRODUCTION OF ANTISERUMS TO PHYTOPATHOGENIC VIRUSES

The method of preservation of potato aucuba mosaic virus and potato virus Y purified preparations immobilized in polyacrylamide gels is provided. The method may be used for preservation of viral antigens for 6 months at room temperature for obtaining a specific antiserums.

Potato aucuba mosaic virus in Potato in New York State

Solanum tuberosum cv. Elmer's Blue is one of a number of heritage potato accessions maintained at Cornell University that exhibit virus-like symptoms of stunting and a leaf yellowing or a mottle mosaic. Testing of this cultivar by double-antibody sandwich (DAS)-ELISA revealed that it was infected with Potato virus S (PVS) but none of the other common potato viruses screened for in North American potato certification programs (3). Mechanical inoculation of sap from potato cv. Elmer's Blue onto Nicotiana debneyii, N. megalosiphon, N. occidentalis, and N. tabacum produced a range of yellowing and mosaic symptoms (symptomless on N. tabacum), indicating the presence of a transmissible agent, but all these hosts tested negative for PVS. To identify possible viruses, reverse transcription (RT)-PCR assays involving generic primers for different groups of viruses were performed on the potato and the Nicotiana spp. Degenerate primers specific to members of the genus Potexvirus (4) amplified a 600-bp region from the symptomatic potato and N. debneyii. Nucleotide sequencing of the RT-PCR amplified product from potato cv. Elmer's Blue (Genbank Accession No. EF609120) and comparisons with GenBank sequences revealed the amplified sequence as having 91% identity with the genomic sequence of Potato aucuba mosaic virus (PAMV; Accession No. S73580). The presence of this virus in potato cv. Elmer's Blue and N. debneyii was confirmed by PAMV-specific antibodies (Agdia, Inc., Elkhart, IN) in a DAS-ELISA format. PAMV is reported to occur worldwide, but uncommonly, with most descriptive work from Europe (2). While this virus has been studied in North America (1,2), these reports employed virus stocks from Europe under experimental conditions or virus in tubers obtained directly from Europe; to our knowledge, there are no unambiguous reports of PAMV in naturally infected North American potato cultivars. By contrast, the PAMV-infected cultivar in this report is a selection originally from a Canadian grower, and although not grown commercially, it is maintained in garden and field plots in New York and other states. References: (1) R. H. Bagnall. Phytopathology 50:460, 1960. (2) G. F. Kollmer and R. H. Larson. Res. Bull. Agric. Exp. Stn. Univ. Wis. 223:1, 1960. (3) S. A. Slack. Page 61 in: Potato Health Management. The American Phytopathological Society. St. Paul, MN, 1993. (4) R. A. A. van der Vlugt and M. Berendsen. Eur. J. Plant Pathol. 108:367, 2002.