Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/1997
Publication Date: N/A
Interpretive Summary: Citrus tristeza virus (CTV) has the largest genome of any plant virus. The size of the CTV genome is similar to that of coronaviruses, which infect only animals and cause serious diseases in animals. Coronaviruses express their genes by a unique mechanism, and this affords an opportunity for controlling the virus. The size of the CTV genome suggested that CTV might express its genes by the same strategy used by coronaviruses, and this would make CTV different from all other plant viruses. Our analysis of CTV gene expression showed that CTV does not share the coronavirus gene expression mechanism, but instead expresses its genes by mechanisms similar to other plant viruses.
Technical Abstract: Citrus tristeza virus (CTV) induces formation of a nested set of at least nine 3' co-terminal subgenomic RNAs (sgRNAs) in infected tissue. The organization and expression of the 19,296-nt CTV genome resembles that of coronaviruses, with polyprotein processing, translational frameshifting, and multiple sgRNA virus polymerases. Both positive-strand RNA virus supergroups, coronaviruses and Sindbis-like viruses, utilize different mechanisms of transcription. To address the mechanism of CTV transcription, 5' termini for the two most abundant sgRNAs, 1.5 and 0.9 kb respectively, were mapped by run-off reverse transcription. The two sgRNAs were demonstrated to have 48- and 38-nt 5'-untranslated regions (UTRs), respectively. The 5' UTR for the 1.5 kb RNA was cloned, sequenced and demonstrated to be co-linear with the 48-nt genomic sequence upstream of the initiator codon of the respective open reading frame 10, i.e., to be of continuous template origin. The data obtained suggest that the sgRNA transcription of CTV is dissimilar from the coronavirus transcription and consistent with the transcriptional mechanism of other Sindbis-like viruses. Thus, the Sindbis-like mechanism of transcription of the positive-strand RNA genomes might be successfully utilized by the genome of up to 19.3-kb with multiple sgRNAs.