XVI International Botanical Congess

The ground state of an imprinted gene is unaltered in the egg and thetwo sperm, but altered in the two polar nuclei. Therefore, genomic imprinting in plants involves the activation of genes in the two polar nuclei during the mitotic divisions following meiosis in the female gametophyte. Since the polar nuclei give rise to the endosperm, genomic imprinting does not result into a heritable changed state and unlike mammalian imprinting requires no resetting. However, epigenetic changes in the embryo can affect the germline and are transmitted equally by both parents. An example is paramutation. However, it is likely that the change of the epigenetic state in genomic imprinting and paramutation is controlled by the same molecular machinery. Therefore, alleles derived from heritable programmed epigenetic states are more suitable for dissecting this molecular machinery than non-heritable ones.