Dual RNA-seq Reveals No Plastic Transcriptional Response Of The Coccidian Parasite Eimeria falciformis To Host Immune Defences

Abstract

BackgroundParasites can either respond to differences in immune defenses that exist between individual hosts plastically or, alternatively, follow a genetically canalized (\"hard wired\") program of infection. Assuming that large-scale functional plasticity would be discernible in the parasite transcriptome we have performed a dual RNA-seq study of the full lifecycle of Eimeria falciformis using infected mice with different immune status (e.g. naive versus immune animals) as models for coccidian infections.\n\nResultsWe compared parasite and host transcriptomes (dual transcriptome) between naive and challenge infected mice, as well as between immune competent and immune deficient ones. Mice with different immune competence show transcriptional differences as well as differences in parasite reproduction (oocyst shedding). Broad gene categories represented by differently abundant host genes indicate enrichments for immune reaction and tissue repair functions. More specifically, TGF-beta, EGF, TNF and IL-1 and IL-6 are examples of functional annotations represented differently depending on host immune status. Much in contrast, parasite transcriptomes were neither different between Coccidia isolated from immune competent and immune deficient mice, nor between those harvested from naive and challenge infected mice. Instead, parasite transcriptomes have distinct profiles early and late in infection, characterized largely by biosynthesis or motility associated functional gene groups, respectively. Extracellular sporozoite and oocyst stages showed distinct transcriptional profiles and sporozoite transcriptomes were found enriched for species specific genes and likely pathogenicity factors.\n\nConclusionWe propose that the niche and host-specific parasite E. falciformis uses a genetically canalized program of infection. This program is likely fixed in an evolutionary process rather than employing phenotypic plasticity to interact with its host. In turn this might (negatively) influence the ability of the parasite to use different host species and (positively or negatively) influence its evolutionary potential for adaptation to different hosts or niches.