Involvement of prophenoloxidases in the suppression of Plasmodium yoelii development by Anopheles dirus.

Anopheles dirus is refractory to a rodent malaria parasite, Plasmodium yoelii, and melanized oocysts are manifested in infected mosquitoes. Prophenoloxidase (PPO) is a zymogen whose active form mediates melanotic encapsulation of invading pathogens in mosquitoes. In this study, we cloned cDNA fragments of four An. dirus PPOs, that are orthologs of Anopheles gambiae PPO2, PPO4, PPO5 and PPO6. AdPPO4 expression in hemocytes was induced in response to P. yoelii infection. RNA interference using double stranded RNA of AdPPO4 led to depletion of its mRNA and other PPO transcripts. This depletion increased P. yoelii infection prevalence and oocyst intensity, and abolished the melanization of oocysts as well. Therefore, An. dirus PPOs may play a role in the refractoriness to P. yoelii.