Genome sequence survey of Paraphysomonas sp. RCC383

Photosynthesis has been gained many times in eukaryotic evolution via endosymbiosis. It has also been lost many times across eukaryotes, including at least 15 times in the chrysophyte algae, a lineage of unicellular algae related to diatoms. This study reveals the functions of non-photosynthetic chrysophyte plastids in 8 lineages that have lost photosynthesis independently. We see a remarkable degree of convergence in retained functions among these chrysophyte lineages. Moreover, the retained functions are highly similar to those of apicomplexans such as the malaria parasite Plasmodium. The shared losses of function provide new insight into the principles of and constraints on plastid reductive evolution, not only within chrysophytes, but across photosynthetic and secondarily non-photosynthetic eukaryotes. Paraphysomonas is the most extreme case of plastid reductive evolution, as it is inferred to have lost its plastid genome.