The role of epigenetics in hybrid vigour

Highlights • Hybrids with similar genome sequences can show significant heterosis. • The final level of heterosis, either in biomass or grain yield, is dependent on changes that occur throughout development. • Hybrids exhibit increased levels of transcription of chloroplast-targeted genes and increases in the size and/or number of photosynthetic cells in cotyledons and early true leaves. • Hybrids show changed 24-nucleotide small interfering RNA levels in localized regions of the genome and altered DNA methylation patterns, which may account for differences in gene expression.