Gametogenesis and the maternal control of embryogenesis have been studied extensively in animal systems at the genetic, molecular, and cellular level. These studies have yielded insight into fundamental concepts and mechanisms involved in the establishment and interpretation of positional information, cell-cell interaction, and signal transduction cascades. In contrast, our knowledge about the genetic and molecular control of these processes in plants is very limited. The simple but highly polar and specialized female gametophyte, which consists of only seven cells belonging to four cell types, make it an ideal system to study the role of positional information and signaling during development. Using Arabidopsis thaliana as a model system, this project focuses on the elucidation of key events during sexual reproduction, namely cell specification, fertilization, and the epigenetic control of seed development with a focus on embryogenesis. We will use a combination of (quantitative) genetic, cell biological, molecular, and computational approaches. The proposed studies will yield insights into fundamental questions: How are cell types specified at the molecular level? Does non-random sister chromatid segregation play a role in differentiation? Are there similarities between distinct signaling cascades? What is the molecular basis of genomic imprinting, which occurs only in mammals and plants? While some of the investigated processes are conserved between animals and plants, others are likely specific, such that the mechanisms can be compared and contrasted to gain new insights into fundamental developmental concepts. Beyond fundamental aspects, however, the proposed studies will contribute to the elucidation of epigenetic mechanisms that transcend plant biology and play a central role in all organisms, including humans, where many diseases have an epigenetic component.