Endosperm and Imprinting, Inextricably Linked

The endosperm is often viewed as a complicated and rather strange tissue: its genome is triploid, it is formed from a second fertilization event specific to flowering plants, and it is a frequent source of incompatibility between plants, yet does not contribute genetic material to the next generation. Additionally, recent investigations have demonstrated that the endosperm is perhaps the most epigenetically divergent plant tissue, with unique DNA methylation and chromatin structure features. Endosperm is also the site of imprinted gene expression, an epigenetic phenomenon intimately linked to endosperm's unusual properties. Imprinted genes are expressed predominantly from either the maternally or paternally inherited allele. This Update focuses on progress over the last several years in understanding imprinted gene expression, from molecular control to physiological significance, within the context of endosperm formation and function.