Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Biology

Supervisor

Dr. Aiming Wang

Abstract

Potyviruses represent the largest genus of plant-infecting viruses and include many agriculturally important viruses such as Turnip mosaic virus (TuMV), Soybean mosaic virus (SMV) and Plum pox virus (PPV). The potyviral genome consists of a large open reading frame (ORF) and a small ORF owing to a translational or transcriptional slippage in the P3 cistron. The polyproteins encoded by these two ORFs are proteolytically processed into 11 mature proteins. Recent studies have shown that P3N-PIPO, the frameshift resulting protein, is a plasmodesmata (PD)-located protein and involved in potyviral cell-to-cell movement by mediating the targeting of the potyviral CI protein to PD to form canonical structures for potyviral cell-to-cell movement. In this study, I introduced in a full-length cDNA infectious clone of TuMV a stop codon or point mutations into P3N-PIPO without affecting the amino acid sequence of other viral proteins including P3 and evaluated effects of these mutations on TuMV infection. It was found that elimination of PIPO or substitution of the positive charged amino acid lysine with the negatively charged amino acid glutamic acid within PIPO compromises TuMV cell-to-cell spreading in Nicotiana benthamiana plants. PEG-mediated transfection assay revealed that virus replication of these mutants is not affected in Nicotiana benthamiana protoplasts. Moreover, transient co-expression of CI and P3N-PIPO mutants showed that the PIPO mutants lose ability to target the TuMV CI protein to plasmodesmata. Subcellular localization of these PIPO mutants indicated that the substitution mutants retain their PD-targeting. These data strongly support that the potyviral P3N-PIPO protein is likely a dedicated protein for potyviral intercellular movement via PD.

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