Molecular Characterization and Bioinformatics Analysis of a Prophenoloxidase-1 (PPO1) in Plutella xylostella

Phenoloxidase (PO) is an important enzyme in insect life, which is involved in important physical functions, such as defensive encapsulation and melanization of foreign organisms and wound healing. In this study, we obtained a cDNA sequence of 2838 bp with 2049 open reading frames encoding 682 amino acids. The protein sequence deduced from the cDNA has high homology with the known PPO1 sequences of other lepidopterous insects. There were three conserved regions, including the two copper-binding sites characteristic of arthropod PPOs. The whole PxPPO1 DNA was also obtained with 7202 bp when the five fragments were stitched together and the overlapping sequences were deleted. The PxPPO1 DNA consists of 11 introns and 12 exons, and the homology is 99.9% when the exons are compared with the above cDNA. Moreover, the gene expression levels were also determined by semiquantitative polymerase chain reaction (PCR), Western blotting, and real-time quantitative PCR; the results indicated that PxPPO1 transcripts in the eggs and the fourth instar larvae were more abundant, followed by the second and the third instar larvae, prepupae, and pupa.