Identification and characterisation of PRXamide peptides in the western flower thrips, Frankliniella occidentalis

Authors: YUN, SEUNG HWAN - Agricultural Research And Extension Service, Korea; JANG, HYO SANG - Oregon State University; AHN, SEUNG-JOON - Mississippi State University; Price, Briana; Hasegawa, Daniel; Choi, Man-Yeon

Submitted to: Insect Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2023
Publication Date: 6/2/2023
Citation: Yun, S., Jang, H., Ahn, S., Price, B.E., Hasegawa, D.K., Choi, M.Y. 2023. Identification and characterisation of PRXamide peptides in the western flower thrips, Frankliniella occidentalis. Insect Molecular Biology. https://doi.org/10.1111/imb.12859.
DOI: https://doi.org/10.1111/imb.12859

Interpretive Summary: Western flower thrips (WFT) is one of the most economically important pests due to its serious damage to agricultural and horticultural crops worldwide. In addition to direct damage from feeding and egg laying on leaves, flowers and fruits, they also transmit tomato spotted wilt virus that is economically important. Insect neuropeptides (NPs) which are small protein molecules produced in nerve tissues and their G-protein coupled receptors (GPCRs) have been suggested as potential targets for new classes of pesticides because they are involved in almost all physiological processes. Recently, insights into genes and proteins of WFT demonstrated a variety of potential control targets, including neuropeptides and GPCRs. In this study, neuropeptides were identified and related to specific WFT behaviors. Results from this study will aid in exploring the biological processes at the molecular level, thus helping to identify biological targets to be utilized for the management of thrips.

Technical Abstract: Insect CAPA and pyrokinin (PK) subfamily peptides are usually produced from two different genes, capa and pyrokinin, respectively. In this study, we identified and characterized the capa and pyrokinin genes from the western flower thrips, Frankliniella occidentalis. The capa gene transcribes three splice variants, capa-a, -b, and -c, encoding two CAPA-PVK peptides (EVQGLFPFPRVamide and QGLIPFPRVamide) and two PK2 peptides (ASWMPSSSPRLamide and DSASFTPRLamide). The pyrokinin gene expects to translate one PK1 (DLVTQVLQPGQTGMWFGPRLamide) and two PK2 peptides (SEGNLVNFTPRLamide and ESGEQPEDLEGSMGGAATSRQLRTDSEPTWGFSPRLamide). The second peptide of PK2 corresponds to the insect PBAN domain and one of the most extended PBAN orthologs in inects. Multiple potential endoproteolytic cleavage sites were presented in the three PK prepropeptides from the pk gene, creating an ambiguity to predict mature peptides. We used GPCRs that are corresponding receptors for CAPA, PK1 and PK2 peptides to solve the difficulty. The three different types of GPCRs were functionally expressed in Sf9 cells and tested to measure binding affinities of the thrips peptides. The binding activities among the receptors and peptides showed that each subfamily peptides exclusively bind to their corresponding receptors, but no or little responses to different family receptors. The binding information was significant for determining the sequences of the CAPA and PK peptides. Our biological method using specific GPCR in this study would be a valuable tool to determine prepropeptides particularly with multiple and ambiguous cleavage sites. Not surprisingly, both capa and pk genes were strongly expressed in the head and thorax, but weakly or barely detected in the abdomen tissues. The two genes were clearly expressed during the immature and adult stages: not the capa expression in the embryo. The whole-mounting immunocytochemistry revealed that the neurons contained PRXamide-like peptides through the head, thorax, and abdomen. Four to six neurosecretory cells were found in the head. Three and seven pairs of immunostained cells were detected in the thorax and abdomen, respectively. It’s unusual that the thrips PK2-2 corresponding to the insect PBAN domains, is the longest case found so far, and that more immunoreactive neurosecretory cell pairs were found in the abdomen, suggesting the PRXamide profiles of Thysanoptera are different from the other insect groups.