Chemosensory Protein 3 Regulates the Behavioural Response of Bradysia Odoriphaga (Diptera: Sciaridae) to Host Plant Volatiles

Abstract

Insects rely on their highly sensitive and precise olfactory system to recognize host plant volatiles and locate host plants. As important proteins in the olfactory system, chemosensory proteins (CSPs) are capable of initial recognition of plant volatiles and binding and transporting useful odor molecules to odor receptors (ORs), and thereby regulating a series of behavioral responses in insects. However, the detailed mechanisms underlying the interaction of host plant volatiles with insect CSPs to regulate behavior remains poorly understood.  Here, we successfully characterized Bradysia odoriphaga chemosensory protein 3 (BodoCSP3), which is richly expressed in adult antennae. Fluorescence competitive binding assays showed that BodoCSP3 has strong binding affinities to two host plant volatiles, 3-thiocyanatoprop-1-ene (Ki = 20.36 ± 0.67μM) and dimethyl trisulfide (Ki = 13.97 ± 0.25μM). Three-dimensional model and molecular docking analysis suggested that BodoCSP3 consists of seven α-helixes and two disulfide bridges, and also revealed key amino acid residues involved in the interaction between BodoCSP3 and 3-thiocyanatoprop-1-ene and dimethyl trisulfide. Site-directed mutagenesis and fluorescence binding assays showed that the amino acid residue Tyr-30 is essential for binding 3-thiocyanatoprop-1-ene and dimethyl trisulfide. Furthermore, RNAi and behavioral assays revealed BodoCSP3 to also be a crucial olfactory protein that participates in modulation of adult B. odoriphaga host plant recognition. These findings demonstrate the potential to develop efficient and environmentally-friendly insect behavioral inhibitors using chemosensory proteins as potential targets of action.

Keywords: Bradysia odoriphaga, chemosensory protein, fluorescence competitive binding assay, site-directed mutagenesis, behavioral bioassays