How Athila retrotransposons survive in the Arabidopsis genome

Background: Transposable elements are selfish genetic sequences which only occasionally provide useful functions to their host species. In addition, models of mobile element evolution assume a second type of selfishness: elements of different familes do not cooperate, but they independently fight for their survival in the host genome. Results: We show that recombination events among distantly related Athila retrotransposons have led to the generation of new Athila lineages. Their pattern of diversification suggests that Athila elements survive in Arabidopsis by a combination of selfish replication and of amplification of highly diverged copies with coding potential. Many Athila elements are non-autonomous but still conserve intact open reading frames which are under the effect of negative, purifying natural selection. Conclusion: The evolution of these mobile elements is far more complex than hitherto assumed. Strict selfish replication does not explain all the patterns observed.