Intraviral homology and subgenomic RNAs of pepper ringspot virus

Subcellular localization of p29, a putative movement protein of pepper ringspot virus

Pepper ringspot virus (PepRSV) is a member of the genus Tobravirus. It possesses a bipartite single-strand RNA genome in a positive-sense polarity. The p29 protein is encoded by RNA 1 and is presumed to be the movement protein (MP) of this virus. In this study, the intracellular distribution of the p29 protein was analyzed by confocal microscopy. Transient expression of the PepRSV p29 protein fused to green fluorescent protein was observed as punctate spots localized next to the cell wall. This protein partially co-localized with the eCFP-tagged tobacco mosaic virus 30K MP, which is known to associate with plasmodesmata. This result suggests that the p29 protein is most probably the movement protein for PepRSV.

Tobraviruses--plant pathogens and tools for biotechnology

The tobraviruses, Tobacco rattle virus (TRV), Pea early-browning virus (PEBV) and Pepper ringspot virus (PepRSV), are positive-strand RNA viruses with rod-shaped virus particles that are transmitted between plants by trichodorid nematodes. As a group, these viruses infect many plant species, with TRV having the widest host range. Recent studies have begun to dissect the interaction of TRV with potato, currently the most commercially important crop disease caused by any of the tobraviruses. As well as being successful plant pathogens, these viruses have become widely used as vectors for expression in plants of nonviral proteins or, more frequently, as initiators of virus-induced gene silencing (VIGS). Precisely why tobraviruses should be so effective as VIGS vectors is not known; however, molecular studies of the mode of action of the tobravirus silencing suppressor protein are shedding some light on this process.

Construction and analysis of infectious transcripts synthesized from full-length cDNA clones of both genomic RNAs of pea early browning virus

Full-length cDNA clones of both RNAs of pea early browning virus have been constructed. Synthetic transcripts derived in vitro from these clones are infectious when inoculated onto plants. Electron microscopy revealed the presence of virions in transcript-inoculated plants, and both purified RNA and virions isolated from such plants could be used to infect other plants. Transcripts of RNA1 alone were able to replicate and spread systemically which is a characteristic of members of the tobravirus group of plant viruses.

Biological activity of transcripts synthesized in vitro from full-length and mutated DNA copies of tobacco rattle virus RNA 2

Full-length cDNA clones of RNA 2 of tobacco rattle virus (TRV) strain PLB have been cloned into the transcription vector pPM1. Products of in vitro transcription by Escherichia coli RNA polymerase, either capped or uncapped, were as infectious as native RNA 2 when coinoculated with RNA 1 of TRV strain TCM. At least 70% of the internal sequence of the cDNA could be deleted without reduction of the replication efficiency of the transcripts. Sequences of 340 nucleotides at the 5' end and 405 nucleotides at the 3' end of PLB RNA 2 were found to be sufficient for replication. The encapsidation of deletion mutants of PLB RNA 2 was investigated after addition of native PLB RNA 1 and RNA 2. Accumulation of these mutants was distinguished from that of wild-type RNA 2 by insertion of nonviral sequences in the deleted parts. Three mutant forms of RNA 2 with extensive deletions in the coat protein (CP) gene were replicated but failed to encapsidate, while mutants with nonviral sequences inserted downstream from the CP gene showed a large reduction in replication efficiency.