Identification and characterization of odorant-binding protein genes in the brown-winged green bug, Plautia stali

The brown-winged green bug, Plautia stali Scott (Hemiptera: Pentatomidae), is a major pest in orchards in Japan and Korea. Large numbers of adults are attracted by aggregation pheromone [methyl (E,E,Z)-2,4,6-decatrienoate] and cause extensive damage to the fruit. To identify olfactory-related genes in P. stali, we performed RNA sequencing (RNA-seq) of adult antennae. Among the 27299 contigs, 16 putative odorant-binding protein (OBP) genes were identified and designated as PstaOBP1-16, including 10 classic (i.e., containing six conserved cysteines) and six Plus-C (i.e., containing more than six cysteines) OBP genes. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) revealed that four genes (PstaOBP1, 3, 6, and 7) were strongly expressed in the antennae. PstaOBP2 was detected throughout the insect body, with higher expression in the antennae, stylet, and tarsus. The remaining OBP genes were expressed in very small amounts. PstaOBP1, which showed the highest expression in adult antennae, was expressed in Escherichia coli (Migula) Castellani & Chalmers cells and the recombinant protein was subjected to a ligand-binding competitive assay. PstaOBP1 bound to methyl (E,E,Z)-2,4,6-decatrienoate with high affinity. Of the other 26 compounds tested, hinokitiol and tropolone bound strongly to PstaOBP1. Hinokitiol is an odor component of hinoki cypress, a host tree of P. stali. Electrophysiological responses to methyl (E,E,Z)-2,4,6-decatrienoate and hinokitiol were detected using adult P. stali antennae. Combined, these results suggest that PstaOBP1 is involved in P. stali responses to pheromone and host plant volatiles.