Evidence for parent-of-origin effects and interparental conflict in seeds of an ancient flowering plant lineage.

Theoretical and empirical studies have long connected the evolutionary innovation of endosperm, a genetically biparental product of a double fertilization process unique to flowering plants (angiosperms), to conflicting parental interests over offspring provisioning. Yet, none of these studies examined interparental conflict in representatives of any of the most ancient angiosperm lineages. We performed reciprocal interploidy crosses in the water lily Nymphaea thermarum, a member of one of the most ancient angiosperm lineages, Nymphaeales. We find that an excess of paternal genomes is associated with an increase in endosperm growth. By contrast, maternal ploidy negatively influences development or growth of all seed components, regardless of paternal genome dosage. Most relevant to the conflict over distribution of maternal resources, however, is that growth of the perisperm (seed storage tissue derived from the maternal sporophyte, found in all Nymphaeales) is unaffected by paternal genome dosage-ensuring maternal control of maternal resources. We conclude that the evolutionary transfer of embryo-nourishing function from a genetically biparental endosperm to a genetically maternal perisperm can be viewed as an effective maternal strategy to recapture control of resource distribution among progeny, and thus that interparental conflict has influenced the evolution of seed development in this ancient angiosperm lineage.