Contribution of introns to the species diversity associated with the apicomplexan parasite, Neospora caninum.

Neospora caninum is an intracellular parasite considered a leading cause of bovine reproduction failure worldwide, and a serious neurological disease of canines. Transplacental transmission in intermediate hosts is considered the most efficient means of transmission, which strictly involves asexual reproduction. Nonetheless, extensive genetic diversity has been reported within the species. What is yet to be elucidated are the major drivers of such diversity, and their impact on important parasite phenotypes such as virulence. Instead of protein-encoding sequences, genome and transcriptome data were used to investigate SNPs in introns between two distinct N. caninum isolates, with reported differences in pathogenicity. Variant analysis identified 840 and 501 SNPs within intergenic regions and introns, respectively, distinctly concentrated on chromosomes VI and XI, whereas the rest of the genome was monomorphic in comparison. Gene ontologies for SNP-dense intron-containing genes included ATP binding, transmembrane transport, protein kinase activity, and transcription and translation processes. This study shows that variation in non-coding DNA is contributing to N. caninum intraspecies genetic diversity, and potentially influencing and contributing to important parasite mechanisms. Finally, we present an assembled and annotated N. caninum apicoplast genome and show that this essential organelle is highly conserved between the two isolates, and related Coccidia.