Reproduction is an event of crucial important in the life cycle of all organisms. The plant life cycle alternates between a diploid and a haploid generation, the sporophyte (spore-producing organism) and the gametophyte (gamete-producing organism). Unlike in animals, where the meiotic products differentiate directly into gametes, the haploid spores of plants undergo several divisions to form the multicellular haploid gametophytes. The differentiation of gametes occurs only later in male and female gametophyte development, respectively. The fusion of egg and sperm during fertilization concludes the gametophytic phase to reconstitute the diploid sporophyte by forming the zygote. Another fusion event between a second sperm and the central cell produces the endosperm, which nourishes the developing embryo. We are using genetic and molecular approaches to identify genes required for the development and function of the female gametophyte in Arabidopsis thaliana focusing on two intimately related areas: (i) the isolation and characterisation of genes involved in female gametophyte development, and (ii) the elucidation of mechanisms involved in the maternal control of the seed development.To elucidate the mechanisms that control gametophyte development at the molecular and genetic level with an emphasis on cell specification and fertilization. Studies directed towards the elucidation of cell specification and signalling processes during plant sexual reproduction address fundamental aspects of development such as the role of positional information, cell lineage, and cell-cell communication. The female gametophyte with its small number of distinct cell types and specific interactions with neighbouring cells and/or the pollen tube is ideally suited to address such questions. A comparison of these mechanisms to other developmental systems will shed light onto common developmental principles.Over the last years, our studies have revealed an extensive regulatory network conferring maternal control over early embryogenesis. We could show that the underlying mechanisms are largely based on epigenetic gene regulation. To gain further insights into how events in the female gametophyte affect embryogenesis we continue to study the role of genomic imprinting and Polycomb group (PcG) proteins in seed development. Epigenetic mechanisms of gene regulation such as genomic imprinting and PcG-mediated repression have taken centre stage in maternal control mechanisms. It becomes increasingly obvious that many processes in development and disease have an epigenetic basis. In terms of basic epigenetic mechanisms, plants are closer to mammals than other model systems: plants use DNA-methylation, chromatin modifications, and RNA-dependent mechanisms for epigenetic regulation, while one or more of these mechanisms are absent in Caenorhabditis elegans, Drosophila melanogaster or yeast. Thus, the understanding of the mechanisms of genomic imprinting in plants and their comparison to mammalian systems will yield insights into fundamental epigenetic mechanisms that transcend plant biology and play a central role in development and disease of all organisms.