Retinoblastoma makes its mark on imprinting in plants

Genomic imprinting results in the preferential expression of alleles from either the maternal or paternal chromosomes. This epigenetic process occurs in embryonic and extra-embryonic (placental) tissues of mammals, but only in the extra-embryonic tissue (the endosperm) of flowering plant seeds. It is thought that imprinting arose to ensure that both maternal and paternal genomes contribute to the development of the offspring [1]. Indeed, the predominant occurrence of imprinting in extraembryonic structures might indicate a similar reproductive strategy in both taxa to correctly regulate embryo growth and development. Because extra-embryonic lineages do not contribute any genetic information to the offspring, it is likely that epigenetic mechanisms responsible for imprinting could evolve rapidly [2,3], without causing deleterious consequences to the offspring