The nucleotide sequences of the RNA 1 and RNA 2 of asparagus virus 2 show a close relationship to citrus variegation virus

Abstract

Asparagus virus-2 (AV-2) is a member of the genus Ilarvirus and infects the vegetable Asparagus officinalis L. The virus is transmitted through seed. Even though the presence of AV-2 causes reductions in vigor and productivity, plants grown from infected seed show no obvious symptoms. The virus has been reported from Europe, North America, and Japan. However, because of the ease with which the virus is seed borne, it has probably been moved to wherever seed lots of asparagus have been distributed [20]. Other ilarviruses are also seed borne and, in addition, have been shown to be transmitted naturally through pollen and the feeding activity of thrips [11]. Ilarviruses are members of the family Bromoviridae. They share traits at the molecular level with the extensively studied cucumoviruses and bromoviruses and have a particularly close relationship to the alfamovirus alfalfa mosaic virus [1]. Ilarviruses possess a tripartite genome of positive-sense ssRNAs. The RNA 1 is monocistronic, coding for a viral replicase. The RNA 2 is bicistronic in some members of the genus but monocistronic in others. The open reading frame (ORF) proximal to the 5 0 UTR codes for the viral polymerase. The second, smaller ORF found in some members of the genus is located toward the 3 0 terminus of the molecule and expressed through a subgenomic RNA that codes for a 2b protein. The initial ORF of RNA 3 codes for the movement protein (MP), and the second ORF of RNA 3 codes for the coat protein (CP). The CP gene is expressed via a subgenomic RNA 4 [7]. AV-2 is a member of subgroup 2 of the ilarviruses, having been shown to be related to the other members of this subgroup: citrus leaf rugose virus (CiLRV), citrus variegation virus (CVV), elm mottle virus (EMoV), spinach latent virus (SpLV), and tulare apple mosaic virus (TAMV), both serologically and at the molecular level [19]. The complete sequence for the RNA 3 of AV-2 has been described [17], as have fragments of sequence for the RNA 1 and RNA 2 [GenBank accessions U93601, U93602, U93603]. Here, we present the complete sequences for the RNA 1 and RNA 2 of AV-2 and discuss the close relationship between this virus and another member of subgroup 2, citrus variegation virus.