International Research Fellowship Program: Isolating Novel Components and Identifying Endogenous Targets of RNA-directed Chromatin Modification

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0502199MosherThe International Research Fellowship Program enables U.S. scientists and engineers to conduct three to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-two-month research fellowship by Dr. Rebecca A. Mosher to work with Dr. David C. Baulcombe at John Innes Centre in Norwich, United Kingdom.RNA-mediated gene silencing, also known as co-suppression, quelling, or RNA interference, is an important genetic regulatory mechanism. The best studied form of RNA-mediated silencing is post-transcriptional gene silencing (PTGS), in which short interfering RNA (siRNA) guide RISC (RNA interference specificity complex) to cleave any mRNA with sequence homology to siRNAs. siRNAs also direct a less understood form of RNA-mediated gene silencing, RNA-directed chromatin modification (RDCM). During RDCM, DNA with homology to siRNAs is methylated, causing a reduction in transcription. Histone H3 is also methylated in response to siRNAs, specifically at lysine 9 (K9), commonly the mark of inert heterochromatin. Through chromatin modification and perhaps other nuclear events, RDCM reinforces PTGS and may also have a developmental function. Genetic screens in Arabidopsis have made deep inroads toward discovering the machinery driving PTGS. In comparison, relatively little is known of the mechanism and associated proteins of RDCM. In specific aim 1 of this proposal, the PI will use mutant analysis to uncover novel components of RDCM. A genetic screen using the PVX-GFP silencing system has uncovered 30 new RDCM mutations falling into at least five complementation groups. These mutations will be cloned using traditional map-based techniques. The natural role of RDCM is also unclear and few endogenous targets have been identified. In specific aim 2, the PI will identify endogenous targets of RDCM using a modified AFLP procedure followed by siRNA analysis and chromatin immunoprecipitation.The Baulcombe group at the Sainsbury laboratory has been pioneers in the field of RNA-mediated silencing and have successfully used genetic analysis to uncover novel elements in RDCM. The Sainsbury Laboratory and greater John Innes Centre is a world-class facility with the equipment and support staff to make this project a success. This project has significant intellectual potential in a number of areas, including basic biology, evolutionary biology, and gene therapy.