Biologically Active Transcripts of a Large Satellite RNA from Arabis Mosaic Nepovirus and the Importance of 5' End Sequences for its Replication

Abstract

Synthetic transcripts of a satellite RNA associated with a lilac isolate of arabis mosaic nepovirus (ArMV) were made from cDNA clones. Transcripts having either six (M1R) or 29 (M3R) extra nucleotides at their 5' ends replicated in the presence of ArMV genomic RNA in manually inoculated Chenopodium quinoa plants, even though M1R also differs from the native sequence at nucleotide position 2. Transcript 12R, which has 11 guanosyl residues and 27 other nucleotides not present in the natural satellite RNA at its 5' end, and also lacks the two 5'-terminal nucleotides (UA), replicated inefficiently, both in transformed tobacco plants and in plants that had been manually inoculated. Transcripts from another construct (M2R) lacking eight 5'-terminal bases of the native sequence did not multiply in plants. Each of these transcripts directed the in vitro synthesis of a protein (Mr 39K) encoded by satellite RNA, although 12R was the least efficient message. Analysis of the 5'-terminal sequences in progeny RNA from M1R showed that the non-native bases were removed and the second nucleotide corrected, suggesting that VPg plus a few initial 5'-terminal bases might serve as a primer for plus-strand synthesis of this satellite RNA. When M1R was inoculated with genomic RNAs from ArMV of ash or ivy, the transcripts replicated and were encapsidated. However, when the same amounts of M1R were inoculated with genomic RNAs of ArMV from hop or sugar-beet, progeny of the transcripts were not detected either in virions or in plants. Less surprisingly, this RNA transcript did not multiply in the presence of dogwood mosaic, strawberry latent ringspot, grapevine fanleaf or cherry leaf roll nepoviruses.