Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/1996
Publication Date: N/A
Interpretive Summary: Citrus tristeza virus (CTV) is the most important and damaging virus infecting citrus plants. CTV is the largest plant virus, and only infects citrus. CTV has twelve genes that enable the virus to infect and cause disease in citrus. This paper describes a study in which the expression of these genes is studied in single cells of sweet orange plants and in tobacco (Nicotiana benthamiana), to define the pattern of and time required for viral gene expression. Characterization of viral genes involved in CTV infection will lead to novel methods to prevent crop losses due to CTV infection.
Technical Abstract: Citrus tristeza virus (CTV), a member of the closterovirus group, is one of the more complex single-stranded RNA viruses. The 5' portion of its 19,296 nt, single-stranded RNA genome is expressed as an 400 kDa polyprotein that is proteolytically processed, while the ten 3' open reading frames are expressed from 3'-coterminal subgenomic RNAs (sg RNAs). We found that the kinetics of accumulation of genomic and sg RNAs and coat protein of the T36 isolate of CTV were similar in protoplasts of the natural host, citrus, and the experimental non-host, Nicotiana benthamiana. Newly synthesized genomic RNA was detected two days postinoculation and increased to a maximum at 3 to 5 days. Most of the abundant sg RNAs also accumulated in parallel to the genomic RNA. However, the smallest sg RNA, which corresponds to the p23 gene, increased earlier. The different sg RNAs accumulated in greatly differing amounts, in general with 3'-most sg RNAs accumulating to higher levels than 5' sg RNAs. However, some 3' sg RNAs (p13 and p18) accumulated to low levels. The two 3'-most sg RNAs (p23 and p20) accumulated to high levels approximately equal to that of the genomic RNA. The accumulation curve for coat protein paralleled that of its mRNA, suggesting that its regulation was transcriptional.