Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Foxtail mosaic virus (FMV) is a member of the potexvirus family which infects primarily monocotyledonous plants. Its flexuous filamentous particles are 500 nm long and consist of a messenger sense RNA encapsidated by a single type of coat protein. We have determined the nucleotide sequence of the FMV gRNA as well as the organization of its coding sequences. The gRNA is 6151 nucleotides long and contains five major open reading frames (ORF). The amino acid sequences of the putative proteins are closely related to homologous proteins of other sequenced potexviruses.;A procedure for the partial purification of the RNA-dependent RNA polymerase (RdRp) complex of FMV from infected leaves of Chenopodium quinoa was established. The products synthesized in vitro by the enzyme were double-stranded RNA molecules. The RdRp preparations obtained could copy RNA templates endogenous to the preparation but were unable to copy added RNA templates. Moreover, potexviral gRNAs specifically inhibited the RNA synthesis activity on endogenous templates. The regions of the genome responsible for the inhibition were identified. Both {dollar}5\sp\prime{dollar} and {dollar}3\sp\prime{dollar} terminal regions of the viral genome were necessary to interfere with RNA synthesis suggesting that this inhibition resulted from a competition for the binding of component(s) of the RdRp complex.;The proteins encoded by ORFs 2, 3, and 4 as well as the coat protein (encoded by ORF5) are believed to play some role in the cell-to-cell movement of potexviruses. We have used a bacterial expression system to produce and purify p26, the protein encoded by ORF2 of FMV, and have determined some in vitro properties of p26. It is an ATP, CTP and RNA binding protein with apparent ATPase activity. An analysis of infected C. quinoa leaves by immunogold electron microscopy using an anti-serum produced against p26 revealed that it is exclusively associated with cytoplasmic inclusions adjacent to aggregates of virus particles. These results suggest that p26 could be involved in the processing of viral RNA or particles prior to their transport rather than being directly involved in their translocation through plasmodesmata.;The distribution of the coat protein in infected C. quinoa was also investigated by immunocytochemistry. Most of the coat protein was localized in the cytoplasm, polymerized into viral particles, but significant amounts were also associated with plasmodesmata. This suggests that the coat protein plays a role in the cell-to-cell movement of potexviruses.



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