Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Aiming Wang

2nd Supervisor

Mark Bernards

Joint Supervisor

Abstract

The Potyvirus genus is the largest group of plant viruses and includes many agriculturally important viruses. The potyviral genome is a single-stranded, positive RNA molecule that contains one long open reading frame (ORF) and another relatively short ORF resulting from transcriptional slippage. The resulting two polyproteins are ultimately processed into 11 mature proteins by three viral protease domains. Of these 11 viral proteins, P1, the very first of the viral polyproteins, is one of the least studied. My research was directed to investigate the functional role(s) of P1 during viral infection. In this study, the localization of P1 within plant cells was investigated and three nuclear localization signals (NLSs) were identified. No interaction was identified between P1 and itself or any of the other 10 viral proteins using yeast two hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. An Arabidopsis cDNA library was used for a Y2H screen with Turnip mosaic virus (TuMV) P1 as bait. Results from this screen yielded 25 putative P1-interacting host factors. Three candidates, AtNDL2, AtTPR and AtUCP3, were chosen for further functional characterization. Homozygous Arabidopsis T-DNA insertion lines for these host factors were obtained and used for TuMV infection assays. AtNDL2, AtTPR and AtUCP3 knockout/knockdown plants demonstrated less susceptibility to TuMV infection, which suggests that those proteins have critical functions in the potyviral infection cycle. These three plant proteins were also recruited into TuMV 6K2 vesicles in virus-infected cells. Besides, the infection ability of Tobacco etch virus (TEV) mutations indicated that P1 may be involved in other non-proteolytic functions such as viral amplification or cell-to-cell transportation. The findings generated in this study may contribute to the development of novel genetic resistance against potyviruses and related plant viruses.

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