Systems-Based Analysis of the Sarcocystis neurona Genome Identifies Pathways That Contribute to a Heteroxenous Life Cycle

Blazejewski, Tomasz; Nursimulu, Nirvana; Pszenny, Viviana; Dangoudoubiyam, Sriveny; Namasivayam, Sivaranjani; Chiasson, Melissa A.; Chessman, Kyle; Tonkin, Michelle; Swapna, Lakshmipuram S.; Hung, Stacy S.; Bridgers, Joshua; Ricklefs, Stacy M.; Boulanger, Martin J.; Dubey, Jitender P.; Porcella, Stephen F.; Kissinger, Jessica C.; Howe, Daniel K.; Grigg, Michael E.; Parkinson, John

Genome comparisons reveal that S. neurona has more orthologs in common with T. gondii than with E. tenella (3,169 versus 1,759 orthologs, respectively), supporting the notion that the Eimeria lineage is more divergent. However, S. neurona is also quite distinct from T. gondii; it possesses only limited genomic synteny, restricted to only dozens of genes, and additionally encodes 1,285 (18%) genes with no detectable homology to any other species. As in E. tenella, LINEs and DNA elements are present in S. neurona, but the DNA elements are significantly expanded in S. neurona, partially accounting for its increased genome size. The presence of the LINEs and DNA elements, however, is not associated with gene model misannotation, since LINEs are as frequently associated with T. gondii orthologs (13.3%) as they are with unique genes (11.6%), indicating that they may drive genome innovations within S. neurona (46) . We did not find any examples of the coronavirus-like long terminal repeat (LTR) element previously associated with the E. tenella genome (21) , strengthening the suggestion that this element was acquired by horizontal gene transfer within that lineage.