Phenoloxidase and its zymogen are required for the larval-pupal transition in Bactrocera dorsalis (Diptera: Tephritidae)

- PO activity and BdPPO1 expression correlated with the development of B. dorsalis.
- PO activity and expression were relatively highest in integument during larval-pupal transition.
- PO is a metalloprotein and was activated by Zn2+, Mg2+, Ca2+, and Cu2+.
- The expression of BdPPO1 was regulated by 20E, resulting in advance pupation.
- RNAi analysis revealed that BdPPO1 plays a key role in the pupation of B. dorsalis.

Phenoloxidases (POs) play a key role in melanin production, are involved in invertebrate immune mechanisms, and are considered important enzymes in the insect development process. In the present study, we report the developmental stage and tissue-specific expression patterns of BdPPO1 and PO activity from Bactrocera dorsalis. The results showed that the activity of PO and its zymogen expression were closely related to the development of B. dorsalis during the larval-pupal transition, particularly in the integument. Additionally, biochemical characterization showed that PO from different developmental stages and tissues all had maximum activity at pH 7.5 and 37 °C. After feeding a metal ion-containing artificial diet, the activity of PO and expression of BdPPO1 were significantly increased, indicating that PO was a metalloprotein and it could be activated by Zn2+, Mg2+, Ca2+, and Cu2+. The functional analysis showed that the expression of BdPPO1 could be regulated by 20-hydroxyecdysone (20E) after injection. Furthermore, injection of the double-stranded RNA of BdPPO1 into the 3rd instar larvae significantly reduced mRNA levels after 24 h and 48 h, and resulted in a lower pupation rate and abnormal phenotype. These results expand the understanding of the important role of PO and its zymogen in the growth of B. dorsalis.