Epigenetic neofunctionalisation and regulatory gene evolution in grasses.

During plant evolution, genome duplication and subsequent selection acting on new gene pairs has frequently resulted in partition of gene functions, or acquisition of new functions. This 'sub- and neofunctionalisation' (subF and neoF) is held to have driven the expansion of key gene classes. One such gene class in maize (Zea mays) includes a pair of Polycomb group (PcG) protein genes that, unlike their single Arabidopsis (Arabidopsis thaliana) counterpart, are both parentally imprinted with only the maternal alleles being expressed in the seed endosperm. Surprisingly, this imprinting is regulated by different mechanisms in the two genes, resulting in different phasing of parent-specific expression. In this opinion article we propose that recruitment of different imprinting systems constitutes 'epigenetic neoF', and has enhanced maternal control over seed development, with a potential impact on the evolution of the large and persistent endosperms of cereal grains.