More than a yolk:: the short life and complex times of the plant endosperm

In most angiosperms, the endosperm is limited to a short phase of the plant life-cycle where it forms part of the seed and plays a major role in its development. Our understanding of this terminally differentiated organ has accelerated in recent years, with discoveries in the fields of phylogeny and developmental genetics shedding light on its evolutionary origin, function and development. Here we explore various conserved and unique features of plant endosperms, including the establishment of distinct functional domains that regulate nutrient transfer from the maternal parent to the developing embryo. We also review data from Arabidopsis and maize that confirm the existence of complex genetic mechanisms operating during endosperm development. Importantly, these findings confirm that, in addition to nourishing the embryo, the endosperm fulfils several other key functions including that of fertilization 'sensor'; detecting and aborting the fertilization products of incompatible or wide hybridizations between related species.