Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Wang, Aiming

2nd Supervisor

Bernards, Mark

Co-Supervisor

Abstract

Viruses are infectious and obligate intracellular parasites. Turnip mosaic virus (TuMV) is a member of the genus Potyvirus which comprises many agriculturally important viral pathogens that threaten crop production. Potyviruses are fully dependent on the host cellular machinery to fulfil their infection cycle in plant hosts. It is well accepted that viral coat protein (CP) is a multifunctional protein that plays key roles in virus propagation and host-virus interactions. This dissertation project aimed to investigate the role of CP in TuMV cell-to-cell movement, to identify the host interactors of TuMV CP, and further to characterize their roles in TuMV infection.

To examine the role of CP in viral cell-to-cell movement, a series of CP deletion and point mutations were introduced into a special TuMV infectious clone that allows for distinguishing primarily and secondarily infected cells. It was found that the core domain and C-terminus of CP are critical for TuMV cell-to-cell movement, but the N-terminal domain is dispensable for TuMV movement and virion assembly. Among cell-to-cell movement defective point mutants, R178A and D222A lost the ability to form detectable virions in protoplasts. The CP protein R178A was not as stable as wild-type CP. Overall, the results revealed the CP determinants of TuMV cell-to-cell movement and suggested that there is a correlation between assembly defects and cell-to-cell movement defects in TuMV biology.

To identify the host interactors of TuMV CP, a yeast two-hybrid screening against Arabidopsis cDNA library was conducted. The screening resulted in the discovery of two novel host proteins, Patellin 3 (PATL3) and Patellin 6 (PATL6) that bind to CP in yeast. TuMV infection assay on PATLs knockout mutants and stable overexpression lines showed that PATL3 and PATL6 negatively regulate TuMV infection. Subcellular localization studies demonstrated that PATL3, but not PATL6, was partially redistributed to viral replication complexes (VRCs) upon TuMV infection. In addition, PATL3 also interacted with the viral protein cylindrical inclusion protein (CI), an essential component of VRCs, suggesting that PATL3 is recruited to the VRC likely through its interaction with CI. Overall, this study identified two host restriction proteins of TuMV that may be manipulated against TuMV and related viruses.

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