Fig. 1

Partial phylogeny of eukaryotes. The genomes of plants, animals, and fungi contain the epigenetic mark H3K9me3 (the lysine residue at position 9 of histone H3 can be tri-methylated). H3K9me3 is thus present in the clades Archaeplastida and Opisthokonta, which have a common ancestor close to the base of all eukaryotes. This suggests that H3K9me3 was already present in early eukaryotes, around the time when retrotransposons appeared in their genomes (phylogeny adapted from [6], showing only the clades that are relevant for the argument)