Sequencing and characterization of two cDNAs putatively encoding prophenoloxidases in the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae)

It has long been suggested that phenoloxidases (EC 1. 14. 18. 1) are very important in a variety of biochemical processes for the successful survival of insects, including cuticular sclerotization, wound healing, and melanotic encapsulation of invading microorganisms. In this study, two prophenoloxidases (PPO, zymogen of phenoloxidase) were identified in the diamondback moth, Plutella xylostella, by native-polyacrylamide gel electrophoresis (PAGE), and their molecular masses were determined by SDS-PAGE. Their cDNAs, PxPPO1 and PxPPO2, were also cloned by reverse transcription polymerase chain reaction (RT-PCR). The full-length cDNAs of PxPPO1 and PxPPO2 encoded 682 and 696 amino acids with calculated molecular masses of 78.3 and 79.7 kDa, respectively. Deduced amino acid sequence identity between the two PxPPOs was only 48.4% whereas identities against other insect PPOs ranged from approximately 40 to 80%. Quantitative real-time PCR analysis showed that the PPO genes were expressed in all developmental stages, with the highest in prepupae; this pattern was consistent with that of PO activity. The level of expression of PxPPO1 was significantly higher than that of PxPPO2 in most developmental stages. These results offer basic knowledge for further study of the function of PPOs in P. xylostella.