Abstract
Different from holometabolous insects, the hemipteran species such as pea aphid Acyrthosiphon pisum exhibit reduced immune responses with the absence of the genes coding for antimicrobial peptide (AMP), immune deficiency (IMD), peptidoglycan recognition proteins (PGRPs), and other immune-related molecules. Prior studies have proved that phenoloxidase (PO)-mediated melanization, hemocyte-mediated phagocytosis, and reactive oxygen species (ROS) participate in pea aphid defense against bacterial infection. Also, the conserved signaling, Jun N-terminal kinase (JNK) pathway, has been suggested to be involved in pea aphid immune defense. However, the precise role of the JNK signaling, its interplay with other immune responses and its regulation in pea aphid are largely unknown. In this study, using in vitro biochemical assays and in vivo bioassays, we demonstrated that the JNK pathway regulated hemolymph PO activity, hydrogen peroxide concentration and hemocyte phagocytosis in bacteria infected pea aphids, suggesting that the JNK pathway plays a central role in regulating immune responses in pea aphid. We further revealed the JNK pathway is regulated by microRNA-184 in response to bacterial infection. It is possible that in common the JNK pathway plays a key role in immune system of hemipteran insects and microRNA-184 regulates the JNK pathway in animals.
Highlights
Insects rely on physiological barriers and innate immune responses to defend themselves against pathogens and parasites
Genomic analysis and biochemical assays revealed that some conserved core components, such as the immune deficiency pathway and peptidoglycan recognition proteins, are missing from the immune system of pea aphid
Through bioinformatics analysis and biochemical assays, we found that these immune responses are under the control of the Jun N-terminal kinase (JNK) pathway and that the latter is regulated by microRNA-184
Summary
Insects rely on physiological barriers and innate immune responses to defend themselves against pathogens and parasites. Upon recognition, signaling pathways such as Toll, immune deficiency (IMD), Jun N-terminal kinase (JNK), Janus kinase/signal transducers and activators of transcription (JAK/STAT), and prophenoloxidase (PPO) pathways are activated [1,2,3,4,5,6]. Activation of these pathways leads to defense responses, such as antimicrobial peptide (AMP) production, reactive oxygen species (ROS) generation, and melanization [1,2,3,4,5,6,7,8]. Hemocytes circulating in the blood participate in cellular responses, such as phagocytosis, encapsulation, and nodulation [11, 12]
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