Epigenetic Reprogramming and Plant Reproductive Development

Seeds represent the next generation in plants and consist of three genetically distinct components: the maternally derived seed coat (brown) and the two products of fertilization, the diploid embryo (green) and the triploid endosperm (yellow). The endosperm nourishes the embryo during seed development and is the caloric foundation of the human diet. Recent insights into genome-wide methylation changes that occur as a programmed part of gamete and seed development represent a first step in understanding the contribution of epigenomic dynamics to successful plant reproduction. The cell that is the female progenitor of the endosperm undergoes genome-wide active DNA demethylation before fertilization, with the largest changes in DNA methylation taking place at repetitive sequences that are normally targeted by RNA-directed DNA methylation in other tissues. Major questions about the functional consequences of DNA demethylation in relation to chromatin structure and transcription remain. Extensive demethylation of the maternal endosperm genome could have profound impacts on chromatin structure and genome function. Furthermore, the temporal and spatial dynamics of epigenomic reprogramming in relation to development are unknown. We are pursuing an understanding of seeds at the epigenomic level from gamete differentiation to seed maturity by integrating data from genome-wide DNA methylation, RNA, and chromatin profiling. A diverse array of genetic and genomic tools makes A. thaliana a powerful model system to understand the basic mechanisms of epigenomic reprogramming in the context of a whole organism.