Geminiviruses and Plant Gene Expression

视网膜母细胞瘤蛋白（retinoblastoma protein，pRb）和E2 F转录因子是动物细胞分裂和分化的关键调节因子。在植物中已经鉴定出了相关的蛋白质，但对其功能知之甚少。在动物中，我们对pRb和E2 F的认识主要来自于对DNA肿瘤病毒及其肿瘤抗原蛋白的研究。这些病毒蛋白与磷酸化不足的pRb（与细胞周期停滞和分化相关的形式）相互作用，破坏pRb/E2 F复合物，导致宿主基因表达改变和细胞周期重入。本研究的总体目标是分析双生病毒感染过程中宿主基因的表达，并以这些重要的植物病毒为工具，研究pR和E2 F如何调控植物基因的表达。第一个目标是建立一个研究双生病毒介导的宿主诱导和pRb相互作用的拟南芥系统。该系统将结合基因组病毒、拟南芥遗传学和数据库工具，研究植物中pRb和E2 F的功能。第二个目的是利用基因表达谱技术研究双生病毒感染对拟南芥基因表达的影响。第三个目标是产生表达野生型和突变型病毒蛋白的转基因植物，这些蛋白仅在pRb结合能力上不同。通过比较这些株系的表达谱，将有助于了解由pRb和E2 F控制的植物基因的同一性。总之，这些实验很可能鉴定出其产物与植物细胞分裂周期、核内复制、分化和疾病相关的基因。这些研究为研究高等真核生物完整成熟组织的去分化过程和细胞分裂周期的恢复提供了一个独特的机会。 它们有可能揭示这两个重要过程的植物特异性成分，并可能通过提供改变植物生长策略的见解对农业产生深远影响。

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.