On epigenetics and epistasis: hybrids and their non-additive interactions

Hybrid seeds have been a key component of greatly increasing the yield of many important crops, foremost of maize. If the parents are properly chosen, non-additive interactions between diverged genomes can lead to strongly superior performance of the F1 progeny, known as hetero-sis. While many different explanations have been advanced, a consensus for the causes of genome-wide positive epistasis in hybrids has not emerged. In this issue of The EMBO Journal, Shivaprasad and colleagues describe a new me-chanism that can account for heterosis often being a gen-ome-wide phenomenon. These authors show that small RNA (sRNA) loci of tomato can exhibit transgressive activ-ity, which can in turn lead to epigenetic and gene expression changes within hybrid progeny. This is particularly exciting because many sRNAs are produced from non-coding region