Evidence of the Involvement of a Plus-C Odorant-Binding Protein HparOBP14 in Host Plant Selection and Oviposition of the Scarab Beetle Holotrichia parallela

SIMPLE SUMMARY: The scarab beetle Holotrichia parallela is a serious underground pest and causes serious damages in China to a variety of crops. To reduce the use of pesticides, insect olfactory proteins attract more and more attention in the development of pollution-free control agents in plant protection. In this study, we evaluate the molecular mechanism in the scarab beetle to detect oviposition cues. We clone a leg biased gene HparOBP14 which encodes for an odorant-binding protein of the scarab beetle and demonstrate its involvement in binding, electrophysiological, and behavioral responses to the oviposition chemicals by the knockdown of HparOBP14 expression using RNA interference technique. Our study provides a strong theoretical basis for the development of environmentally acceptable strategies for H. parallela control. ABSTRACT: Holotrichia parallela is one of the agriculturally important scarab beetle pests in China. In this study, HparOBP14 was cloned, which is the most abundantly expressed among the OBP genes in the legs of female H. parallela adults. Sequence comparison and phylogenetic analysis showed that HparOBP14 has a Plus-C structure motif. The expression profile analysis revealed that HparOBP14 expression was the highest in the female antennae and then in the legs. The fluorescence competitive binding experiment of the recombinant HparOBP14 protein showed that HparOBP14 had an affinity with 6-methyl-5-heptene-2-one (plant volatile), 3-methylindole, p-cymene, methanol, formaldehyde, α-pinene, and geraniol (organic fertilizer volatile). Knockdown HparOBP14 expression decreased significantly the EAG response of the injected female adults to p-cymene, methanol, formaldehyde, α-pinene, and geraniol. Similarly, the injected female adults were significantly less attracted to geraniol and methanol. Therefore, HparOBP14 might bind organic matter volatiles during oviposition. These results are not only helpful to analyze the olfactory recognition mechanism of female adult H. parallela when choosing suitable oviposition sites, but also to provide target genes for green prevention and control of H. parallela in the future.