A novel virus from Macrosiphum euphorbiae with similarities to members of the family Flaviviridae

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Abstract
A virus with a large genome was identified in the transcriptome of the potato aphid (Macrosiphum euphorbia) and was named Macrosiphum euphorbiae virus (MeV-1). The MeV-1 genome is 22,780 nt, including 3' and 5' non-coding regions, with a single large open reading frame encoding a putative polyprotein of 7,333 amino acids. The C-terminal region of the predicted MeV-1 polyprotein contained sequences with similarities to helicase, methyltransferase and RNA-dependent RNA polymerase (RdRp) motifs, while the N-terminal region lacked any motifs including structural proteins. Phylogenetic analysis of the helicase placed MeV-1 close to pestiviruses, while the RdRp region placed it close to pestiviruses and flaviviruses, suggesting MeV-1 has a positive polarity single-stranded RNA genome and is a member of the family Flaviviridae. Since the MeV-1 genome is predicted to contain a methyltransferase, a gene present typically in flaviviruses but not pestiviruses, MeV-1 is likely a member of the Flavivirus genus. MeV-1 was present in nymphal and adult stages of the aphid, aphid saliva and plant tissues fed upon by aphids. However, the virus was unable to multiply and spread in tomato plants. In addition, double-stranded RNA, the replication intermediate of RNA viruses, was isolated from virus-infected M. euphorbiae and not from tomato plants infested with the aphid. Furthermore, nymphs laid without exposure to infected plants harbored the virus, indicating that MeV-1 is an aphid-infecting virus likely transmitted transovarially. The virus was present in M. euphorbiae populations from Europe but not from North America and was absent in all other aphid species tested.

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