Intellectual Merit. This project concerns mechanisms by which plant hosts recognize viral pathogens and initiate specific defenses. The research is focused on a family of DNA-containing plant viruses known as geminiviruses. In plants, RNA silencing is an important antiviral defense that results in specific degradation of viral mRNA. In the case of DNA viruses, a related process (RNA-directed methylation) leads to the methylation of viral DNA and associated histone proteins that together constitute the viral chromosome. Methylation typically leads to gene silencing, and recent work from this laboratory has demonstrated that cellular pathways used to methylate endogenous cellular genes and viral DNA are essentially identical. In this project, geminiviruses will be employed as models to further study the RNA-directed methylation pathway. Specifically, the roles of cellular RNA polymerases II, IV, and V in de novo methylation of viral genomes will be examined using a combination of genetic and biochemical approaches. The DNA sequence features that recruit these enzymes to the viral chromosome, the methylation status of the sequences that they recognize, and the nature of the non-coding RNAs that they generate will be investigated. In addition, the geminivirus system will be used to identify and characterize cellular proteins that recognize methylation marks on chromatin and translate these into changes in gene expression. Methylation controls cellular gene expression during normal development, and is important for organizing inactive regions of cellular chromosomes and silencing potentially damaging invasive DNAs. Thus studying geminivirus chromatin methylation promises to increase our understanding of viral pathogenesis and of fundamental processes that govern the activity of cellular chromatin. Broader Impacts. A better understanding of host antiviral defenses will eventually lead to the development of plants that are better able to withstand or resist virus attack. This project will integrate research and education by contributing to the training of visiting scientists, postdoctoral associates, graduate students, and undergraduate students, some of whom are underrepresented minorities. In addition, the PI participates in the NSF REU Program sponsored by the Department of Molecular Genetics at Ohio State University, and in the OSU Summer Practical Workshop in Plant Functional Genomics, which attracts international and domestic students, postdocs, young faculty, and high school teachers and trains them in basic techniques and principles of molecular biology and genomics. The PI has also contributed materially by donating antibodies to a new, soon-to-be-launched Plant Antibody Facility. As Director of the campus-wide interdisciplinary graduate program in Molecular, Cellular, and Developmental Biology (MCDB, currently ~130 PhD students) for the past 16 years, the PI has a long history of promoting graduate education. Efforts include an active role in recruiting minority students through the Graduate School's SROP Program and the University Office of Diversity and Inclusion. The PI also has an active interest in enabling interactions between faculty and students and annually co-organizes the MCDB Seminar Series, the Interdisciplinary Graduate Program Symposium, and the First-Year Graduate Student Seminar, which includes training in research ethics.
