Plant Responses to Virus Replication

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This research investigates the mechanisms of replication and pathogenesis of plant viruses, particularly the tobacco mosaic virus (TMV). Studies involve the significance of ubiquitination of the TMV coat protein to the viral infection process. This includes looking at the appearance of ubiquinated coat protein in the free pool of cytosolic coat proteins, localizing the site of the ubiquinated protein both on the TMV viruon and within infected cells, looking at the ubiquination of coat protein in transgenic plants and characterizing the response of plant cells to viral infection by monitoring the cell's production of ubiquitin. A second area of experimentation involves the mechanism whereby viral nucleic acids and proteins become established in the chloroplast during the process of viral infection. Specific experiments are designed 1) to ascertain whether mature viral coat protein enters the chloroplast from the cytosol or is synthesized within the chloroplast from viral RNA and 2) to investigate the mechanism by which viral RNA is incorporated into the chloroplast. The long-term goal of this work is an increased understanding of the mechanisms by which plant viruses bring about pathogenic responses in infected plant cells. Emphasis will be placed on the tobacco mosaic virus (TMV). The first goal involves investigating the significance of the finding that TMV (and numerous other viruses) contain the protein ubiquitin attached to intact virus particles. Ubiquitin is a small protein found in the cells of all higher plants and animals. It is known to form covalent attachments to selected proteins in numerous cells and plays a role in cell regulation, protein degradation and stress responses. A second goal of this research addresses the observation that TMV RNA is able to enter the chloroplast during infection which is coupled with the fact that the chloroplast is the major site of cellular disruption during TMV infection. Studies will focus on how the viral RNA gets into the chloroplast. This problem will be approached initially by developing a cell-free system for looking at the uptake of viral RNA by isolated chloroplasts. Once this system is operating, more specific aspects of the RNA uptake can be addressed experimentally.