In this recent essay, I discussed studies that showed a surprisingly high rate of movement of DNA from organelles to the nuclear genome. Curious and questioning readers should have wondered about this, as one implication is that nuclear genomes should become huge mosaics of organelle DNA in a relatively short evolutionary time. Of course, this is not the case – organelle DNA may be found in nuclear genomes, but it makes up a tiny fraction of these genomes.
If you had read my essay and wondered along these lines, you may pat yourself on the back. For this paradox is something that has puzzled others. A recent paper in PLoS Genetics helps to resolve things. Briefly, Anna Sheppard and Jeremy Timmis followed up on the earlier studies , asking what happens to the organelle genes after they wander into the nucleus. These authors found a high frequency with which the organelle DNA (at least the marker gene that was followed in these studies) is altered or deleted. As the authors discuss (the abstract follows beneath the fold), this suggests that the overall picture is a dynamic one – DNA can move into the nucleus at a high rate, but it is also removed relatively rapidly. The result is a sort of steady state, one that affords the creation of new nuclear genes without the burden of vast amounts of organelle DNA.