Fancy a gene? A surprisingly complex evolutionary history of peroxiredoxins

While the phylum Apicomplexa includes “only” several thousand described species of obligatory parasites of animals, it may in fact be the most specious group of parasitic protists with over a million species [1]. The best known representatives are Plasmodium spp., Toxoplasma gondii and Cryptosporidium spp., which belong to the most important and widespread human parasites exacting an enormous disease burden. On the other hand, dinoflagellates and colpodellids, which are monophyletic with the apicomplexans, are ecologically highly significant, as they belong to the most abundant marine protists [2]. As the common ancestor of these groups was most likely a free-living photosynthesizing protist, one wonders, which evolutionary forces contributed to the dramatic transition of some of its descendants into the arguably most successful intracellular parasites? Although a range of various processes and mechanisms contributed to this transition, most likely it also involved an acquisition of genes via horizontal gene transfer (HGT), which might have provided typical characteristics of a parasitic cell, such as immune escape, nutritional dependence and the capacity to invade other cells.

HGT is a movement of DNA between two different organisms that allows them to gain novel features different from those which can be passed from a parent to an offspring. Being most widespread in eubacteria, it impacts the composition of their genomes to such an extent that multigene phylogenetic analyses form a net instead of a tree, demonstrating their extreme mosaicism. HGT also played the most crucial role in eukaryotic evolution, as it enabled gene transfer from endosymbionts to the host nucleus, contributing to the emergence of extant mitochondria and plastids. As a result of this development, organellar genomes encode only a small fraction of organellar proteins, with the vast majority of them being encoded by the nuclear genome. The proteins are then post-translationally imported to the organelles using complex targeting signals [3].

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We acknowledge the use of research infrastructure that has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 316304.