Functional characterization of Niemann–Pick proteins type C2 as odorant carriers in Neoseiulus barkeri olfactory perception

Arthropods utilize olfactory function to detect informational substances within their natural habitats, thereby facilitating essential life activities such as foraging, mating, and oviposition. Niemann-Pick protein type C2 (NPC2), a putative odorant carrier, has not been fully described in the olfactory perception of predatory mites. In this study, we characterized in detail the olfactory perception functions of NbNPC2-2 and NbNPC2-3 in the important predatory mite Neoseiulus barkeri. The results show that 2 NPC2 proteins, with 6 conserved cysteine sites, are significantly upregulated (by 2.93-fold for NbNPC2-2 and 1.66-fold for NbNPC2-3) with methyl salicylate (MeSA), an important herbivore-induced plant volatile (HIPV). Knocking down both NbNPC2-2 and NbNPC2-3 prevented N. barkeri from preferring pest-infested plants, and reduced their crawling speed to 2.92 and 3.12 mm/s under MeSA treatment. The affinity analysis revealed that NPC2-2 binds to HIPVs β-ionone, MeSA, and ocimene (Ki = 28.55 ± 2.12, 40.73 ± 3.89, and 45.15 ± 2.22, respectively), and NPC2-3 binds to 4-ethylbenzaldehyde (Ki = 51.67 ± 0.23). Molecular docking further confirmed hydrogen bonding interactions between NPC2-2, NPC2-3, and these HIPVs. These results indicated that NPC2-2 and NPC2-3 act as odor carriers involved in the olfactory perception of mites toward HIPVs. This enhances understanding of the molecular mechanism of phytoseiid olfaction.