Phylogenomics identifies a new major subgroup of apicomplexans, Marosporida class. nov., with extreme apicoplast genome reduction

Varsha Mathur, Waldan K Kwong, Filip Husnik, Nicholas A T Irwin, Árni Kristmundsson, Camino Gestal, Mark Freeman, Patrick J Keeling, Geoff McFadden
2020 Genome Biology and Evolution  
The phylum Apicomplexa consists largely of obligate animal parasites that include the causative agents of human diseases such as malaria. Apicomplexans have also emerged as models to study the evolution of non-photosynthetic plastids, as they contain a relict chloroplast known as the apicoplast. The apicoplast offers important clues into how apicomplexan parasites evolved from free-living ancestors and can provide insights into reductive organelle evolution. Here, we sequenced the
more » ... and apicoplast genomes of three deep-branching apicomplexans, Margolisiella islandica, Aggregata octopiana and Merocystis kathae. Phylogenomic analyses show that these taxa, together with Rhytidocystis, form a new lineage of apicomplexans that is sister to the Coccidia and Hematozoa (the lineages including most medically significant taxa). Members of this clade retain plastid genomes and the canonical apicomplexan plastid metabolism. However, the apicoplast genomes of Margolisiella and Rhytidocystis are the most reduced of any apicoplast, are extremely GC-poor, and have even lost genes for the canonical plastidial RNA polymerase. This new lineage of apicomplexans, for which we propose the class Marosporida class nov., occupies a key intermediate position in the apicomplexan phylogeny, and adds a new complexity to the models of stepwise reductive evolution of genome structure and organelle function in these parasites.
doi:10.1093/gbe/evaa244 pmid:33566096 pmcid:PMC7875001 fatcat:pcj5vzave5arjcjearkm7ke4v4