1. DEMETER, Goddess of the Harvest, Activates Maternal MEDEA to Produce the Perfect Seed 
Hugh Dickinson, Rod Scott 
Molecular Cell 
Volume 10, Issue 1, Pages 5-7 (July 2002)
DOI: /S (02)

2. Figure 1 Model for DEMETER Action
In plants, the female (embryo sac) and male (pollen grain) gametophytes are produced by meiosis and mitosis in the ovule and anther, respectively. The embryo sac contains two gametes, an egg, and a pair of polar nuclei. The pollen grain contains two sperm. Fertilization of the fused polar nuclei (now the central cell nucleus) by one of the two sperms produces a primary endosperm nucleus, which divides repeatedly to form the endosperm. In the endosperm of wild-type Arabidopsis thaliana plants, MEDEA is expressed from the maternal allele only; the paternal allele is silenced or “imprinted.” Choi et al. (2002) suggest that this is achieved through the activity of DEMETER: expression of the DEMETER gene is required to prevent silencing of the MEDEA gene in the endosperm (for example by removing methylated cytosine residues in the promoter that would otherwise attract a chromatin condensing complex), but is only expressed in the female gametophyte. Absence of DEMETER in the male gametophyte results in an unmodified paternal MEDEA allele, which is subsequently silenced in the endosperm. This balance of active to inactive MEDEA alleles results in a normal sized endosperm: loss of DEMETER or MEDEA should produce the same mutant phenotype lethal overproliferation and autonomous endosperm development.
Molecular Cell  , 5-7DOI: ( /S (02) )