Efficient translation of Eggplant mottled dwarf nucleorhabdovirus N and X genes requires both 5' and 3' UTRs.

BACKGROUND: Circularization of RNA mediated by association of translation factors and RNA elements in 5' and 3' UTRs is a common feature for translation control in eukaryotes. There is no information about translation in plant rhabdoviruses and little information is known in animal rhabdoviruses. METHODS: The role of 5' and 3' UTRs in two genes of EMDV in translation were studied using luciferase constructs and RNA structures of these sequences were analyzed by SHAPE and Inline probing. RESULTS: We have found that efficient translation of N and X mRNAs of nucleorhabdovirus Eggplant mottled dwarf virus (EMDV) requires elements present in both 5' and 3' UTRs. Luciferase reporter constructs containing precise 5' and 3' UTRs of the N and X genes had substantially higher translational activity compared with constructs containing only the 5' or 3' UTR. The 3'UTR of carmovirus Turnip crinkle virus, which contains a well-characterized cap-independent translation enhancer, was unable to complement the lack of EMDV 3' UTR. Addition of cap analog to luciferase constructs containing the UTRs of the N gene did not restore translation, and translation of the reporter construct in the absence of the 5' cap was higher than the capped construct. No RNA-RNA interactions between 5' and 3' UTRs were detected by EMSA or in-line cleavage structural assays. Deletion of 11 nucleotides from the 3' terminus negated the synergistic activity of the 3'UTR. CONCLUSIONS: The results with RNA-RNA interaction suggesting that translational synergy between the UTRs may utilize alternative means. Mutation analysis in 3'UTR suggesting that the polyadenylation signal sequence contained in this location may play a critical role in translation.

Maize Iranian mosaic virus shows a descending transcript accumulation order in plant and insect hosts.

Maize Iranian mosaic virus (MIMV) is a distinct member of the genus Nucleorhabdovirus. In this study, expression of all MIMV genes in maize for four weeks after inoculation and in inoculative planthoppers was examined using a quantitative RT-PCR (RT-qPCR) assay. Accumulation of MIMV P, gene 3, M, G and L transcripts relative to N transcripts was measured and normalized to 18S rRNA in maize plants and to the ribosomal protein S13 gene (RPS13) in planthoppers using the comparative CT method. In plants, higher levels of MIMV N transcripts were found relative to other transcripts, while MIMV L transcripts were at the lowest levels. The highest accumulation of MIMV transcripts was found at 14 days postinoculation (dpi). At 21 dpi, we found the lowest transcript levels for all genes, which increased again at 28 dpi, although in lower amounts than at 14 dpi. In Laodelphax striatellus, MIMV M, G and L transcripts accumulated at lower levels than other transcripts. The gene 3 transcript level was high in both plants and planthoppers. Our results showed that transcript accumulation for the MIMV genes was similar in both hosts and followed the pattern of sequential transcriptional attenuation from the 3' to the 5' end of the genome, similar to vertebrate rhabdoviruses. These results indicate that the regulation of virus gene transcription for this plant-infecting rhabdovirus is similar to that of some vertebrate-infecting rhabdoviruses.