Due to the ubiquity of microbes in the environment, it is assumed that most organisms must be able to protect themselves from microbial pathogens. Recent genomic analyses of defense mechanisms in arthropods suggest conservation of key elements underlying responses to pathogens and parasites. At the center of pathogen-induced immune response are signaling pathways triggered by the recognition of fungal, bacterial and viral signatures. These pathways signal the production of effector molecules, such as antimicrobial peptides and lysozymes, which degrade or destroy invaders. We have used a combination of gene annotation of the recently available pea aphid (Acrythosiphon pisum) genome, functional genomics and classical immunological approaches to compare the immune response of aphids to that of other insects.
Results/Conclusions

Strikingly, pea aphids appear to be missing genes thought critical for recognition, signaling and microbial degradation in insects. In line with results of gene annotation, experimental analyses designed to characterize response of immune-challenged aphids uncovered evidence for few immune-related products. Though these analyses suggest that aphids may be limited in their ability to protect themselves, these animals may thrive nonetheless because of their frequent association with protection-conferring bacterial symbionts. Therefore, both microbial ecology and genomics reveal key aspects of disease ecology in this system.