Submitted to: Virology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/4/1997
Publication Date: N/A
Citation: Interpretive Summary: Tobacco etch virus was used as a vector to study the expression of several genes of beet yellows virus and their impact on TEV infection. When capsid, the 20-kDa or HSP70 homolog proteins were cloned into the TEV and the recombinant virus subsequently inoculated onto Nicotaina tabacum there was not a detectable effect on the movement of TEV in the plants and the cloned genes were stable in these plants. In contrast, when the leader proteinase of BYV (L-Pro) was cloned into the TEV the systemic movement and accumulation of the TEV was severely limited. The progeny virus containing the L-Pro underwent various deletions that overcame the defects in virus spread. Engineered mutants of L-Pro showed that the central domain was responsible for changes in virus accumulation but the whole L-Pro was required for debilitation of systemic movement. When the L-Pro TEV recombinants were inoculated onto N. benthamiana there was no major changes in movement of the virus. These results suggests a possible new means of engineering resistance to virus in the potyvirus group.
Technical Abstract: A tobacco etch virus (TEV)-based expression vector has been used for insertion of several ORFs derived from the unrelated beet yellows virus (BYV). Hybrid TEV variants expressing the BYV capsid protein, 20-kDa protein, or HSP70 homolog systemically infected Nicotiana tabacum and stably retained BYV sequences. In contrast, insertion of the ORF encoding BYV leader proteinase (L- Pro) resulted in severely impaired systemic transport and accumulation of recombinant TEV. Progeny of this virus underwent various deletions affecting the L-Pro sequence and mitigating the defects in virus spread. Model experiments involving several spontaneous and engineered mutants indicated that the central domain of BYV L-Pro was responsible for the defect in hybrid virus accumulation, whereas full-size L-Pro was required for maximal debilitation of systemic transport. Strikingly, BYV L- Pro expression did not debilitate systemic infection of hybrid TEV in Nicotiana benthamiana plants. No major defects in replication of encapsidation of recombinant RNA were revealed in N. tabacum protoplasts. These results indicated that BYV- L-Pro specifically interfered with TEV systemic transport and accumulation in a host-dependent manner and suggested a potential utility of closterovirus L-pro as an inhibitor of potyvirus infection. In addition, it was demonstrated that the 107-amino- acid-residues-long N-terminal part of the TEV helper component proteinase is not essential for systemic infection.