Turnip yellow mosaic virus is a monopartite, plus sense RNA virus
infecting the Cruciferae, and is a model system for the study of RNA virus
replication. A cDNA clone (pTYMC) representing an infectious RNA
genome of the European isolate of TYMV was constructed and used to assess
the importance of virus genes in virus infectivity.
Derivatives of pTYMC with alterations in open reading frame 69 (ORF-
69) were made. The mutations disrupted the expression of ORF-69 in vitro as
predicted. Although the ORF-69 mutants were competent for replication in
protoplasts, none of the mutants detectably infected turnip or Chinese cabbage
plants, except where reversion mutations led to the restoration of an
uninterrupted ORF-69. The data suggest a role for ORF-69 expression in the
cell-to-cell movement of the virus.
Mutant RNAs with a deletion or frameshift in the coat protein ORF
infected protoplasts and plant leaves. No systemic infection symptoms were
generated by these mutants, and no viral products were detected in young,
expanding tissue of infected plants. When the coat protein deletion mutant
and an ORF-69 mutant were co-inoculated onto plants, only a virus
producing a coat protein of wild type size was detected in symptomatic,
systemic tissue in these inoculations, emphasizing a requirement for the
expression of native size coat protein for the systemic translocation of TYMV
infection.
The role of ORF-206 expression in TYMV replication was examined.
Three classes of mutants were made in ORF-206: those affecting the synthesis
of the 150 kDa protein, those affecting the synthesis of the 70 kDa protein, and
those affecting the synthesis of both the 150 and the 70 kDa proteins. All ORF-
206 mutations eliminated RNA infectivity. Protoplast inoculations using
mixtures of individual ORF-206 mutant RNAs and a helper genome
demonstrated that co-replication of defective genomes could occur.
Moreover, inoculations in which individual 150 kDa and 70 kDa protein
mutant RNAs were combined showed that complementation between these
two classes of mutants was possible. The data indicate that RNAs expressing
wild type 150 kDa protein are favored replication substrates in mixed
infections, and suggest that the 150 kDa protein functions preferentially in cis. / Graduation date: 1993
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36154 |
| Date | 10 April 1992 |
| Creators | Weiland, John J. |
| Contributors | Dreher, Theo W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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