Identification and characterization of pyrokinin and CAPA peptides, and corresponding GPCRs from spotted wing drosophila, Drosophila suzukii.

The family of FXPRLamide peptides serves as a major insect hormone. It is characterized by a core active amino acid sequence conserved at the C-terminal ends, and provides various physiological roles across the Insecta. In this study we identified and characterized pyrokinin (PK) and CAPA cDNAs encoding two FXPRLamide peptides, pyrokinin and CAPA-DH (diapause hormone), and two corresponding G protein-coupled receptors (GPCRs) from spotted wing drosophila (SWD), Drosophila suzukii. Expressions of PK and CAPA mRNAs were differentially observed during all life stages except the embryo, and the detection of CAPA transcription was relatively strong compared with the PK gene in SWD. Both D. suzukii pyrokinin receptor (DrosuPKr) and CAPA-DH receptor (DrosuCAPA-DHr) were functionally expressed and confirmed through binding to PK and DH peptides. Differential expression of two GPCRs occurred during all life stages; a strong transcription of DrosuPKr was observed in the 3rd instar. DrosuCAPA-DHr was clearly expressed from the embryo to the larva, but not detected in the adult. Gene regulation during the life stages was not synchronized between ligand and receptor. For example, SWD CAPA mRNA has been up-regulated in the adult while CAPA-DHr was down-regulated. The difference could be from the CAPA mRNA translating multiple peptides including CAPA-DH and two CAPA-PVK (periviscerokinin) peptides to act on different receptors. Comparing the genes of SWD PK, CAPA, PKr and CAPA-DHr to four corresponding genes of D. melanogaster, SWD CAPA and the receptor are more similar to D. melanogaster than PK and the receptor. These data suggest that the CAPA gene could be evolutionally more conserved to have a common biological role in insects. In addition, the effect of Kozak sequences was investigated by the expression of the GPCRs with or without Kozak sequences in Sf9 insect cells. The Kozak sequenced PK receptor was significantly less active than the original (= no Kozak sequenced) receptor. Our results provide a knowledge for potential biological function(s) of PK and CAPA-DH peptides in SWD, and possibly offer a novel control method for this pest insect in the future.