Polycomb group (PcG) protein. PcG proteins act by forming multiprotein complexes, which are required to maintain the transcriptionally repressive state of homeotic genes throughout development. PcG proteins are not required to initiate repression, but to maintain it during later stages of development. They act via the methylation of histones, rendering chromatin heritably changed in its expressibility (PubMed:23150632, PubMed:27133784). Together with EZ1 and CLF forms a complex that is involved in gene transcriptional repression by trimethylation on histone H3 'Lys-27' (H3K27me3) of target genes (PubMed:23150632). Involved in the regulation of embryo and seed endosperm development. FIE1-containing PcG complex in seed endosperm regulates the expression of various transcription factors by trimethylation on histone H3 'Lys-27' (H3K27me3) of target genes. Involved in the overall expression regulation of nutrient metabolism genes, such as prolamin synthesis and seed storage protein synthesis genes. Can regulate valine, leucine and isoleucine metabolism-related genes (PubMed:27133784). Interacts with EZ1 and CLF (PubMed:23150632). Component of the polycomb repressive complex 2 (PRC2), which methylates 'Lys-27' residues of histone H3 (H3K27me3), leading to transcriptional repression of the affected target gene (PubMed:23150632). Expressed specifically in seed endosperm. The FIE1 locus is imprinted. Maternal inherited gene is expressed in the ovule (the egg and the central cell), while the paternal inherited gene is silenced in the pollen. After fertilization, only the maternal inherited allele is expressed (PubMed:19825651). The gain-of-function epi-allele (Epi-df) plants exhibit dwarf phenotype, defect in flower development and very poor seed set (PubMed:23150632). Plants silencing FIE1 have delayed embryo development, reduced seed set, and reduced grain length, width and weight (PubMed:27133784). Belongs to the WD repeat ESC family.