The role of epigenetics in hybrid vigour

Hybrid vigour, or heterosis, refers to the increased yield and biomass of hybrid offspring relative to the parents. Although this has been exploited in plants for agriculture and horticulture, the molecular and cellular mechanisms underlying hybrid vigour are largely unknown. Genetic analyses show that there are a large number of quantitative trait loci (QTLs) that contribute to the heterotic phenotype, indicating that it is a complex phenomenon. Gene expression in hybrids is regulated by the interactions of the two parental epigenetic systems and the underlying genomes. Increasing understanding of the interplay of small RNA (sRNA) molecules, DNA methylation, and histone marks provides new opportunities to define the basis of hybrid vigour and to understand why F1 heterosis is not passed on to subsequent generations. We discuss recent findings that suggest the existence of several pathways that alter DNA methylation patterns, which may lead to transcriptional changes resulting in the heterotic phenotype.