http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Replication and translation of Panicum mosaic virus
xiv, 194 leaves : illustrations ; 28 cm.
Panicum mosaic virus (PMV) is single-stranded, positive-sense RNA virus in the Tombusviridae that affects lawn, forage, and feed grasses. PMV is an excellent model for studying virus replication and translation in plants because it is the only virus that supports two different satellites, satellite panicum mosaic virus (SPMV) and satellite RNAs. In addition, PMV uses a combination of translation strategies to produce six proteins. Grasses make up the largest and perhaps the most economically and nutritionally important group of plants worldwide. Although grasses are susceptible to a wide range of plant viruses, few of these are well characterized at the molecular level, further supporting the use of PMV as a model system. This dissertation examines the role two 5'-proximal PMV-encoded proteins, p48 and p112, that are necessary and sufficient for replication of PMV and SPMV in millet protoplasts. Alanine scanning mutagenesis of a Tombusviridae-specific domain in the p48 gene affected PMV and SPMV accumulation, possibly due to a defect in replicase assembly and/or template recognition. The PMV coat protein (CP) and RNA elements within the subgenomic (sg) RNA portion of the virus also contributed to PMV accumulation. Purification experiments suggested that the PMV CP associates with the replicase complex, which would partially explain its role in replication. The efficient translation of the p48 and p112 proteins from the PMV genomic (g) RNA is dependent on an RNA element in the 3'-untranslated region (UTR) of the gRNA and sgRNA. Disruption of this 3'-translational element (TE) disrupted translation, but was partially restored when this cis-acting TE was moved to another part of the PMV genome. PMV replication also appeared to be affected by sequences in the 3'-UTR. Maize mild mottle virus (MMMV) was characterized and found to share many genome features with PMV, but it has a larger host range. Molecular comparisons between MMMV, which was identified in Nigeria, and PMV may elucidate specific regions of each virus that regulate host range, translation, replication, movement, and symptom development. The experiments described in this dissertation provide a foundation for further development of the PMV+SPMV system to study molecular plant-virus interactions in grasses.
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Includes bibliographical references (leaves 165-186).