In flowering plants, seed development begins with the fertilization of theegg cell and the central cell by the male gametes, giving rise to thediploid embryo and the triploid endosperm, respectively. Although thegenome present in the embryo and the endosperm is identical, the fate ofboth fertilization products is different. In most species, the endosperminitially develops as a syncytium, where nuclear divisions are notfollowed by cellular divisions. After a defined number of mitotic eventsthe endosperm begins to cellularize and to differentiate into specificsubdomains. Embryo and endosperm development occur coordinated andinfluence each other. Mutants of the fertilization independent seed (fis)class have defects in co-ordinated development of embryo and endosperm. Infis mutants endosperm development can initiate in the absence of afertilization signal. If fertilization occurs, the endosperm proliferatesabnormally and the embryo aborts. The FIS genes encode Polycomb group(PcG) proteins, a class of proteins that ensure the mitotically stablerepression of their target genes. The type I MADS-box gene PHERES1 (PHE1)has been shown to be a direct target gene of the FIS complex, suggestingan important role of PHE1 during seed development. Our research aims arei) Elucidate the function of PHE1 and closely related homologs of PHE1 bygeneration and analysis of double and multiple mutants. ii) Identifytarget genes for PHE1 and PHE2. iii) Identify DNA methylation marks at thePHE1 locus and elucidate the establishment of these marks during seeddevelopment and compare the profile in different mutant backgrounds. iv)Identify upstream regulators of PHE1 expression. To reach our researchgoals we will apply genetic screens, molecular and biochemical approachesand genomic profiling techniques. The goal of the project is to gain adeeper understanding of seed development in general and to reveal thefunction of type I MADS-box genes during reproductive development. Asseeds are our main food source, the investigation of seed development hasalso a great economical impact. Furthermore, using the PcG target genePHE1 as a tool we will investigate the mechanism of PcG mediatedrepression. As PcG complexes are conserved in animals and plants, theresult of these studies will be of general interest for the scientificcommunity.