Gene cloning and expression patterns of two prophenoloxidases from Catantops pinguis (Orthoptera: Catantopidae)

In insect, fat body plays major roles in insect innate immunity. Phenoloxidase (PO) is an important component in insect innate immunity and is necessary for acclimatization. In our study, two prophenoloxidase (PPO) subunits were obtained from fat body of Catantops pinguis (Stål). The full-length cDNA sequence of one PPO (CpPPO1) consisted of 2347 bp with an open reading frame (ORF) of 2187 bp encoding 728 amino acids, while the other subunit (CpPPO2) had a full length of 2445 bp, encoding 691 amino acids. Both the PPO gene products are predicted to possess all the structural features of other PPO members, including two putative tyrosinase copper-binding motifs with six highly conserved histidine residues and a thiolester-like motif. Tissue distribution analysis showed that both PPO mRNAs were abundantly expressed in the fat body among 11 tissues examined, and they were transiently up-regulated after Escherichia coli infection, consistent with them being immune-responsive genes. Total levels of CpPPO1 and CpPPO2 mRNA transcripts were much higher in first instar larvae and adults. A much higher transcript level of CpPPO1 was detected in several months, while there were extremely high mRNA expression levels of CpPPO2 in January, July, October, and December. The above results suggested that PPO from fat body might also bring significant function during the processes of development and acclimatization for C. pinguis.