The Polycomb group (PcG) chromatin remodelling proteins have conserved roles in the stable maintenance of gene expression patterns. In Arabidopsis, mutations in the genes of the FERTILIZATION INDEPENDENT SEED (FIS) PcG complex cause seed abortion when maternally inherited. In the case of two FIS-class gene mutations, seed abortion occurs because these genes(MEA and FIS2) are paternally imprinted in the endosperm. On , Leroy and colleagues now report that the FIS gene MSI1 is not similarly imprinted; MSI1 is bi-allelically expressed in the embryo and endosperm, and its early paternal expression does not rescue msi1mutant seeds. By contrast, its expression in msi1 mutant female gametophytes (which enclose the female gamete) does restore seed development. From their findings, the authors conclude that an intact FIS complex is required in the female gametophyte to maintain normal gene expression patterns in the central cell (from which the endosperm develops). In its absence,endosperm defects occur that cause both embryo arrest and seed abortion.
