Veritable powerhouses – even without DNA

This reduction is especially pronounced in that part of the genome that lies outside the nucleus. In plants and algae, their own DNA is not just found in the nucleus and mitochondria, but also in the plastids, which they need for photosynthesis. For dinoflagellates in general, this plastid DNA is fairly basic, and consists of only 14 genes. Yet Amoebophrya ceratii would appear to have done away with the plastids entirely, and with all but one of their genes.

Yet the ‘budget cuts’ that the parasite has pursued with regard to its mitochondria are even more impressive. In related species, these tiny power plants’ DNA still contains three genes, which experts have generally assumed to be indispensable. But Amoebophrya ceratii has apparently cut out the mitochondria genome entirely; despite painstaking efforts, the team was unable to find any trace of it. Two of the three genes are nowhere to be found, and the third, cytochrome c oxidase 1 (COX1 or COI), has migrated to the nucleus. “That absolutely amazed me,” says Uwe John, “because there’s no other oxygen-breathing life-form on record that has no genetic material of its own in its mitochondria.” 

This downsizing could come in handy when the parasites need to rapidly form a large number of new dinospores. According to Uwe John, “Perhaps it’s then more effective to regulate all processes using the nucleus. This is likely also the most efficient way to use the host’s resources.” But none of this would do any good if the energy supply broke down. Yet that seems unlikely: the mitochondria work quite well in all stages, even allowing the dinospores to swim rapidly when looking for a host. “Apparently, these parasites have found a strategy all their own when it comes to energy production,” AWI researcher Uwe John summarises. “To produce energy, they require only part of the five know protein complexes found in the mitochondria of human beings and all animals.”

The experts hope that their findings will help us understand the evolution of the dinoflagellates and their relatives. This would also be interesting because the latter include other parasites and the pathogens that cause diseases like malaria. In addition, the findings could offer new insights into the evolutionary histories of mitochondria and plastids: both were originally independent life forms, which were absorbed by other single-celled organisms in the primordial past, and lived on inside them as so-called endosymbionts. With the passage of time, their genetic material was gradually reduced and they essentially became ‘service providers’ that were no longer capable of surviving on their own. Yet Amoebophrya ceratii appears to have taken this development one step further, and taken away the last vestiges of its endosymbionts’ genetic autonomy.