Phenoloxidases Are Required for the Pea Aphid Defense against Bacterial and Fungal Infection.

The pea aphid Acyrthosiphon pisum has an incomplete immune system compared to those of other insect species; some conserved components and pathways in other species are missing in the pea aphid genome. As a core component of insect immune system, prophenoloxidase (PPO) genes are retained in the pea aphid. Early studies have also shown the presence of phenoloxidase (PO) activity in specific tissues or cells in the pea aphid and suggested its involvement in response to immune challenges. In this study, we knocked down the expression of PPO genes in the pea aphid using dsRNA-based interference and, quantitative PCR analysis and an enzyme activity assay confirmed our success in the PPO gene knockdown. In the bacterial and fungal infection experiments, we observed that the knockdown of PPO resulted in more live bacterial cells and fungal spores in the body of the aphids and higher mortality of the aphids after infection. Our study provided evidence supporting a critical role of PPO in the defense of the pea aphid. This article is protected by copyright. All rights reserved.