Identification and Expression Analysis of G-Protein-Coupled Receptors Provide Insights into Functional and Mechanistic Responses to Herbivore-Induced Plant Volatiles of Paracarophenax alternatus

Abstract

Herbivore-induced plant volatiles (HIPVs) play a pivotal role in mediating tritrophic interactions between plants, herbivores, and their natural enemies. Paracarophenax alternatus, a parasitic mite targeting the egg stage of Monochamus alternatus, has emerged as a promising biocontrol agent. However, its ability to detect Pinus massoniana-derived HIPVs for host insect localization remains unclear. G-protein-coupled receptors (GPCRs) may play a role in mediating the perception of HIPVs and associated chemosensory signaling pathways in mites. In this study, a total of 85 GPCRs were identified from P. alternatus. All GPCRs exhibited conserved transmembrane domains and stage-specific expression patterns, with 21 receptors significantly upregulated in viviparous mites. Combined with two previously identified odorant receptors (ORs), six candidate chemosensory receptors were selected for molecular dynamics simulations to validate their binding stability with key volatile compounds. The results demonstrate that specific GPCRs likely facilitate HIPV detection in mites, enabling precise host localization within dynamic ecological niches. Our findings provide critical insights into the molecular basis of mite-host interactions and establish a framework for optimizing P. alternatus-based biocontrol strategies against pine wilt disease vectors.

Keywords: G-protein-coupled receptor; Monochamus alternatus; Paracarophenax alternatus; biocontrol; pine wilt disease.

Figure A1

ERRAT assessment results of protein models in P. alternatus. ** p < 0.01 (reject null hypothesis).

Figure A2

Ramachandran plots of protein models in P. alternatus. Note: the red area is the optimal area, the brown yellow area is the permissible area, the bright yellow area is the barely reasonable area, and the earthy yellow area is the unreasonable area.

Figure 1

Phylogenetic maximum-likelihood tree of GPCR families from P. alternatus and other mite species.

Figure 2

The motif compositions of the GPCR proteins and their distribution in P. alternatus. (A) The identified conserved motifs of the 85 GPCR proteins in P. alternatus. (B) The sequences of the 10 motifs detected by the MEME online tool. (C) The number of conserved motifs identified in each GPCR family. (D) A Venn diagram of the motifs detected in domain subfamilies A, B, C, and F (https://www.bioinformatics.com.cn/, accessed on 23 January 2025).

Figure 3

A schematic diagram of the P. alternatus GPCR domain. Blue boxes indicate the 7TM-GPCRs domain. Red boxes indicate the other domain.

Figure 4

A heatmap showing the relative expression levels of 85 GPCR genes in P. alternatus across three distinct physiological states: 72 h developed physogastric state (PHY), viviparous state (VIV), and phoretic state (PHO). Rows were scaled by Z-score normalization (TBtools) to highlight stage-specific expression patterns. The color gradient reflects standardized expression levels (red: high; blue: low). Hierarchical clustering was applied to rows and columns using Euclidean distance and complete linkage.

Figure 5

The relative expression levels of the upregulated genes in viviparous mites (VIV), 72 h developed physogastric mites (PHY), and phoretic mites (PHO). Data are presented as the means ± standard errors (SEM), and statistical comparisons were based on Student’s t-tests. p < 0.01 (**).

Figure 6

Three-dimensional structure model of docking protein in P. alternatus. Red indicates negative electrostatic potential regions (negatively charged), blue represents positive electrostatic potential regions (positively charged), and white corresponds to neutral regions.

Figure 7

Molecular docking simulations of GPCR proteins with five active ligands. (A) Interaction diagram of α-Pinene–PaltSKR-1. (B) Interaction diagram of β-Pinene–PaltSKR-1. (C) Interaction diagram of longifolene–PaltSKR-1. (D) Interaction diagram of β-Caryophyllene–PaltTKR-2. (E) Interaction diagram of β-Phellandrene–PaltOR-1.