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Dept of Molecular Genetics |
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My laboratory is engaged in a long term effort to understand, in molecular terms, the mechanisms by which geminiviruses carry out and regulate their DNA replication and gene expression programs. Because geminiviruses rely to a large extent on the metabolic machinery of the host cell, we anticipate obtaining important insight into plant gene expression and DNA replication in the course of our studies. Another laboratory goal is the elucidation of specific mechanisms involved in the transmission of geminiviruses by their whitefly vectors. Plant to plant transmission is a key component of agronomically important geminivirus diseases. We also expect this study to provide new insight into the evolution of host-virus-vector interactions. In other work, we are developing improved geminivirus- based vectors for the expression of novel proteins in plants and are engaged in research to engineer plants for broad-based resistance to geminivirus infection. Most of our studies involve tomato golden mosaic virus (TGMV) and beet curly top virus (BCTV). Like all geminiviruses, TGMV and BCTV package small circular ssDNA genomes into paired (twinned or geminate) isometric particles. Viral ssDNA replicates in the nucleus of the host cell via a rolling circle mechanism that employs dsDNA intermediates. Current work is primarily focused o the functions of individual viral gene products. We have learned that the viral AL2 protein (TrAP) is a transcription factor that is necessary for expression of the coat protein gene. Coat protein gene expression requires activation in some tissues (mesophyll) and de-repression in others (vascular tissue). Both activation and de-repression appear to be mediated by TrAP through interactions with different host proteins. We aim to identify these host proteins, and to characterize their interactions with TrAP and the transcription machinery. We are also attempting to identify host genes whose expression is stimulated by this potent viral activator and to assess the role of host gene activation in viral pathogenesis. Another project is concerned with the viral AL3 protein, which functions as a replication enhancer. The AL3 gene and protein are being subjected to a combined genetic and biochemical analysis in order to determine exactly how enhancement occurs. Recently, we discovered that AL3 protein binds AL1 protein, a factor that is essential for the initiation of viral DNA replication. We are interested in determining the significance of this interaction, and are attempting to identify host proteins with which AL3 protein might also interact. In collaboration with the laboratory of Dr. Judith Brown, we have recently initiated a project to study the mechanisms by which geminiviruses are transmitted between plants by their whitefly vectors. More precisely, we are interested in identifying regions of the coat protein that are required for transmission and the insect proteins that interact with coat protein to potentiate this highly specific process. |
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