Alveolate mitochondrial metabolic evolution: dinoflagellates force reassessment of the role of parasitism as a driver of change in apicomplexans.

Mitochondrial metabolism is central to the supply of ATP and numerous essential metabolites in most eukaryotic cells. Across eukaryotic diversity, however, there is evidence of much adaptation of the function of this organelle according to specific metabolic requirements and/or demands imposed by different environmental niches. This includes substantial loss or retailoring of mitochondrial function in many parasitic groups that occupy potentially nutrient-rich environments in their metazoan hosts. Infrakingdom Alveolata comprises a well-supported alliance of three disparate eukaryotic phyla-dinoflagellates, apicomplexans, and ciliates. These major taxa represent diverse lifestyles of free-living phototrophs, parasites, and predators and offer fertile territory for exploring character evolution in mitochondria. The mitochondria of apicomplexan parasites provide much evidence of loss or change of function from analysis of mitochondrial protein genes. Much less, however, is known of mitochondrial function in their closest relatives, the dinoflagellate algae. In this study, we have developed new models of mitochondrial metabolism in dinoflagellates based on gene predictions and stable isotope labeling experiments. These data show that many changes in mitochondrial gene content previously only known from apicomplexans are found in dinoflagellates also. For example, loss of the pyruvate dehydrogenase complex and changes in tricarboxylic acid (TCA) cycle enzyme complement are shared by both groups and, therefore, represent ancestral character states. Significantly, we show that these changes do not result in loss of typical TCA cycle activity fueled by pyruvate. Thus, dinoflagellate data show that many changes in alveolate mitochondrial metabolism are independent of the major lifestyle changes seen in these lineages and provide a revised view of mitochondria character evolution during evolution of parasitism in apicomplexans.