A paper in Nature Genetics describes a mutation in a tomato gene that leads to fruits that don’t ripen. This would be an important discovery in itself–the ripening of fruits is certainly an economically interesting trait–but a further twist makes it even more interesting. The twist: the mutation is actually an epimutation. That is, the two alleles–the non-ripening allele and the wild type allele–have no difference is sequence, but rather a difference in the methylation status of the promoter. The methylated allele is expressed at a lower level, leading to an inhibition of ripening.
Also interesting is that the methylation status of the allele seems to be fairly stable– they claim to have seen a tomato revert from the non-ripening phenotype to wild type three times in 3000 plants grown since 1993. So this epimutation acts essentially in a Mendelian fashion. Whether this will be a common occurrence in plants (or other taxa) remains to be seen.