Rhoptry Proteins ROP5 and ROP18 Are Major Murine Virulence Factors in Genetically Divergent South American Strains of Toxoplasma gondii.

TitleRhoptry Proteins ROP5 and ROP18 Are Major Murine Virulence Factors in Genetically Divergent South American Strains of Toxoplasma gondii.
Publication TypeJournal Article
Year of Publication2015
AuthorsBehnke, MS, Khan, A, Lauron, EJ, Jimah, JR, Wang, Q, Tolia, NH, L Sibley, D
JournalPLoS Genet
Volume11
Issue8
Paginatione1005434
Date Published2015/08/31
ISSN1553-7404
KeywordsAmino Acid Sequence, Animals, Animals, Outbred Strains, DNA Copy Number Variations, Molecular Sequence Data, Phylogeny, Protein Interaction Domains and Motifs, Protozoan Proteins, Quantitative Trait Loci, Rodent Diseases, South America, Toxoplasma, Toxoplasmosis, Animal, Virulence, Virulence Factors
Abstract

Toxoplasma gondii has evolved a number of strategies to evade immune responses in its many hosts. Previous genetic mapping of crosses between clonal type 1, 2, and 3 strains of T. gondii, which are prevalent in Europe and North America, identified two rhoptry proteins, ROP5 and ROP18, that function together to block innate immune mechanisms activated by interferon gamma (IFNg) in murine hosts. However, the contribution of these and other virulence factors in more genetically divergent South American strains is unknown. Here we utilized a cross between the intermediately virulent North American type 2 ME49 strain and the highly virulent South American type 10 VAND strain to map the genetic basis for differences in virulence in the mouse. Quantitative trait locus (QTL) analysis of this new cross identified one peak that spanned the ROP5 locus on chromosome XII. CRISPR-Cas9 mediated deletion of all copies of ROP5 in the VAND strain rendered it avirulent and complementation confirmed that ROP5 is the major virulence factor accounting for differences between type 2 and type 10 strains. To extend these observations to other virulent South American strains representing distinct genetic populations, we knocked out ROP5 in type 8 TgCtBr5 and type 4 TgCtBr18 strains, resulting in complete loss of virulence in both backgrounds. Consistent with this, polymorphisms that show strong signatures of positive selection in ROP5 were shown to correspond to regions known to interface with host immunity factors. Because ROP5 and ROP18 function together to resist innate immune mechanisms, and a significant interaction between them was identified in a two-locus scan, we also assessed the role of ROP18 in the virulence of South American strains. Deletion of ROP18 in South American type 4, 8, and 10 strains resulted in complete attenuation in contrast to a partial loss of virulence seen for ROP18 knockouts in previously described type 1 parasites. These data show that ROP5 and ROP18 are conserved virulence factors in genetically diverse strains from North and South America, suggesting they evolved to resist innate immune defenses in ancestral T. gondii strains, and they have subsequently diversified under positive selection.

DOI10.1371/journal.pgen.1005434
Alternate JournalPLoS Genet
PubMed ID26291965
PubMed Central IDPMC4546408
Grant ListR01 AI082423 / AI / NIAID NIH HHS / United States
R01 AI118426 / AI / NIAID NIH HHS / United States
AI036629 / AI / NIAID NIH HHS / United States
R01 AI036629 / AI / NIAID NIH HHS / United States
AI118426 / AI / NIAID NIH HHS / United States