XVI International Botanical Congess

In flowering plants, endosperm develops following fusion of the 2x central cell and a 1x sperm, giving a ratio of 2 maternal to 1 paternal genomes. This ratio is essential for normal seed development, reflecting the activity of imprinted (uniparentally expressed) genes. In crosses between Arabidopsis plants of different ploidies, endosperm development was abnormal, with maternal and paternal excess producing complementary phenotypes, including changes to a) mitotic rate during the free nuclear phase, b) timing of cellularisation, c) behaviour of chalazal endosperm. These changes resulted in small endosperms in seeds with an excess of maternal genomes, and large endosperms in seeds with paternal excess. In mammals, imprinting involves allele specific DNA methylation. We will present evidence that DNA methylation also plays an important role in imprinting in plants.