Effect of RNA interference mediated knockdown of prophenoloxidase subunit 2 on immune response in wild silkmoth, Antheraea mylitta

Activation of phenoloxidase cascade is an important immune response in insects. Phenoloxidase (PO) is synthesized by the hemocytes as an inactive zymogen, pro-phenoloxidase (proPO) which is then activated by proteolytic cleavage to active phenoloxidase (PO). proPO cascade which triggers melanization in many invertebrates is intimately associated with cellular immune responses by aiding phagocytosis, nodulation, and encapsulation. But in some insects the proPO system is not essential for survival and does not seem to be dependent on microbial infection. Although PO pathway is linked to nodulation and melanization of nodules, the exact molecular mechanism modulating it, is still not well defined. The objective of this study is to elucidate the effect of RNA interference mediated knockdown of prophenoloxidase on immune responses in a wild silkmoth Antheraea mylitta. We used a 144 bp sequence of A. mylitta proPO corresponding to proPO subunit 2 of other insects for knockdown assay. RNA interference mediated knockdown of proPO subunit 2 has resulted in a significant increase in the bacterial load and reduced nodule formation in the larvae of A. mylitta. The results provide deep insight into the role of proPO in the nodulation response.