The haploid multicellular male gametophyte of plants, the pollen grain, is a terminally differentiated structure whose function ends at fertilization.Unlike pollen grains, the immature gametophyte retains its capacity for totipotent growth when cultured in vitro.Haploid embryo production from cultured immature male gametophytes is a widely used plant breeding and propagation technique that was described nearly 50 years ago, but one that is poorly understood at the mechanistic level.We have used a chemical genomics approach to determine the role of epigenetic modifications in the establishment of cell totipotency from the male gametophyte in Brassica napus and arabidopsis.The results of this screen will be presented.