Olfactory proteins and floral scent synthases mediate the specificity of fig-wasp mutualism

The obligate mutualism between fig trees and their pollinating fig wasps provides a classical model for investigating coevolution. While olfactory cues are crucial for fig wasps to locate their host figs, the molecular mechanisms underlying species-specific recognition remain poorly understood. Here, we demonstrate that host fig trees dynamically regulate their volatile emission across developmental stages by highly expressing attractant synthases, such as linalool synthase (LINS), during the receptive phase, while upregulating repellent synthases, including 1,8-cineole synthase (1,8-CINS), following pollination. Fluorescence competitive binding assays indicated that odorant-binding proteins (OBPs) from both pollinating and non-pollinating fig wasps could bind host volatile compounds, but pollinator OBPs exhibited distinct binding profiles and markedly higher binding affinities. Consistent with these molecular differences, behavioral assays further showed that Ceratosolen solmsi marchali and C. gravelyi were strongly attracted to indole and linalool yet repelled by 1,8-cineole. Furthermore, molecular docking and site-directed mutagenesis identified Phe109 in CsolOBP1 and Phe117 in CgraOBP1 as key amino acid residues mediating high-affinity ligand binding. Together, our results reveal an integrated regulatory pathway linking host volatile biosynthesis, olfactory recognition, and behavioral responses, providing mechanistic insight into how precise chemical communication maintains the specificity and stability of this highly specialized mutualism.