title: Diversification of MIF immune regulators in aphids: link with agonistic and antagonistic interactions.
abstract: BACKGROUND
  The widespread use of genome sequencing provided evidences for the high degree of conservation in innate immunity signalling pathways across animal phyla. However, the functioning and evolutionary history of immune-related genes remains unknown for most invertebrate species. A striking observation coming from the analysis of the pea aphid Acyrthosiphon pisum genome is the absence of important conserved genes known to be involved in the antimicrobial responses of other insects. This reduction in antibacterial immune defences is thought to be related to their long-term association with beneficial symbiotic bacteria and to facilitate symbiont maintenance. An additional possibility to avoid elimination of mutualistic symbionts is a fine-tuning of the host immune response. To explore this hypothesis we investigated the existence and potential involvement of immune regulators in aphid agonistic and antagonistic interactions.
  
  
  RESULTS
  In contrast to the limited antibacterial arsenal, we showed that the pea aphid Acyrthosiphon pisum expresses 5 members of Macrophage Migration Inhibitory Factors (ApMIF), known to be key regulators of the innate immune response. In silico searches for MIF members in insect genomes followed by phylogenetic reconstruction suggest that evolution of MIF genes in hemipteran species has been shaped both by differential losses and serial duplications, raising the question of the functional importance of these genes in aphid immune responses. Expression analyses of ApMIFs revealed reduced expression levels in the presence, or during the establishment of secondary symbionts. By contrast, ApMIFs expression levels significantly increased upon challenge with a parasitoid or a Gram-negative bacteria. This increased expression in the presence of a pathogen/parasitoid was reduced or missing, in the presence of facultative symbiotic bacteria.
  
  
  CONCLUSIONS
  This work provides evidence that while aphid's antibacterial arsenal is reduced, other immune genes widely absent from insect genomes are present, diversified and differentially regulated during antagonistic or agonistic interactions.
authors.forename: Géraldine
authors.initials: G
authors.lastname: Dubreuil
authors.forename: Emeline
authors.initials: E
authors.lastname: Deleury
authors.forename: Didier
authors.initials: D
authors.lastname: Crochard
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Simon
authors.affiliation: Sophia Agrobiotech Institute, INRA-CNRS-UNS, UMR 7254, 400 Route des Chappes, 06 903 Sophia Antipolis, France. Christine.coustau@sophia.inra.fr.
authors.forename: Christine
authors.initials: C
authors.lastname: Coustau
mesh_terms: D000818:Animals; D001042:Aphids / Q000235:genetics* / Q000276:immunology / Q000382:microbiology / Q000469:parasitology; D005075:Biological Evolution; D019295:Computational Biology; D015870:Gene Expression; D005786:Gene Expression Regulation; D049750:Genome, Insect; D054884:Host-Pathogen Interactions / Q000235:genetics / Q000276:immunology; D056747:Immunomodulation / Q000187:drug effects / Q000235:genetics*; D008263:Macrophage Migration-Inhibitory Factors / Q000819:agonists / Q000037:antagonists & inhibitors / Q000145:classification / Q000235:genetics*; D005810:Multigene Family; D010802:Phylogeny; D013559:Symbiosis
chemical_list: D008263:Macrophage Migration-Inhibitory Factors