Abstract
The innate immune system in insects is regulated by specific signalling pathways. Most immune related pathways were identified and characterized in holometabolous insects such as Drosophila melanogaster, and it was assumed they would be highly conserved in all insects. The hemimetabolous insect, Rhodnius prolixus, has served as a model to study basic insect physiology, but also is a major vector of the human parasite, Trypanosoma cruzi, that causes 10,000 deaths annually. The publication of the R. prolixus genome revealed that one of the main immune pathways, the Immune-deficiency pathway (IMD), was incomplete and probably non-functional, an observation shared with other hemimetabolous insects including the pea aphid (Acyrthosiphon pisum) and the bedbug (Cimex lectularius). It was proposed that the IMD pathway is inactive in R. prolixus as an adaptation to prevent eliminating beneficial symbiont gut bacteria. We used bioinformatic analyses based on reciprocal BLAST and HMM-profile searches to find orthologs for most of the “missing” elements of the IMD pathway and provide data that these are regulated in response to infection with Gram-negative bacteria. We used RNAi strategies to demonstrate the role of the IMD pathway in regulating the expression of specific antimicrobial peptides (AMPs) in the fat body of R. prolixus. The data indicate that the IMD pathway is present and active in R. prolixus, which opens up new avenues of research on R. prolixus-T. cruzi interactions.
Highlights
The immune system of arthropods relies exclusively on an innate response triggered by the detection of conserved Pathogen Associated Molecular Patterns (PAMPs) found on the surface of microorganisms [1]
We confirmed that all orthologs were transcribed using PCR amplification of cDNAs generated from fat body tissues of immune activated insects or by finding their transcripts in published transcriptomes [40,49]
RpDREDD and rpIKKβ, not currently annotated in the R. prolixus genome could not be amplified using PCR, but were found in published transcriptomes. rpCYDL is partially annotated in the R. prolixus genome (RPRC014665) but spans 3 contigs that are assembled in opposing directions, breaking the gene into 3 unlinked fragments
Summary
The immune system of arthropods relies exclusively on an innate response triggered by the detection of conserved Pathogen Associated Molecular Patterns (PAMPs) found on the surface of microorganisms [1]. The immune deficiency pathway in Rhodnius prolixus collection and analysis, decision to publish, or preparation of the manuscript
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