Geminiviruses and Plant Gene Expression

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The retinoblastoma protein (pRb) and the E2F transcription factors are key regulators of celldivision and differentiation in animals. Related proteins have been identified in plants, but little isknown about their functions. In animals, much of our knowledge of pRb and E2F is from studiesof DNA tumor viruses and their tumor antigen proteins. These viral proteins interact withunder-phosphorylated pRb (the form associated with cell cycle arrest and differentiation) anddisrupt pRb/E2F complexes, leading to altered host gene expression and cell cycle reentry.Recent experiments suggested that geminiviruses use a similar mechanism to alter cell cyclecontrols in plants. The overall goals of this research are to analyze host gene expressionduring geminivirus infection and to use these important plant viruses as tools to study how pRband E2F regulate plant gene expression. The first aim is to develop an Arabidopsis system forstudying geminivirus-mediated host induction and pRb interactions. This system will combinegeminiviruses with Arabidopsis genetic and database tools to study pRb and E2F function inplants. The second aim is characterize the global changes in Arabidopsis gene expressionassociated with geminivirus infection using gene profiling technology. The third aim is togenerate transgenic plants that express wild type and mutant viral proteins that differ only in theirpRb binding capacities. Comparison of the expression profiles of these lines will provide insightinto the identities of plant genes controlled by pRb and E2F. Together, these experiments arelikely to identify genes whose products are associated with the cell division cycle,endoreduplication, differentiation, and disease in plants. The studies represent a unique opportunity to study the dedifferentiation process and the return to the cell division cycle in intact mature tissues of a higher eukaryote. They have the potential to uncover plant-specific components of these two important processes and may have a profound impact on agriculture by providing insight into strategies for altering plant growth.