Date Published: July 21, 2017
Publisher: Public Library of Science
Author(s): Yong Peng, Shan-Ning Wang, Ke-Ming Li, Jing-Tao Liu, Yao Zheng, Shuang Shan, Ye-Qing Yang, Rui-Jun Li, Yong-Jun Zhang, Yu-Yuan Guo, Patrizia Falabella.
Odorant binding proteins (OBPs) and chemosensory proteins (CSPs) play important roles in transporting semiochemicals through the sensillar lymph to olfactory receptors in insect antennae. In the present study, twenty OBPs and three CSPs were identified from the antennal transcriptome of Microplitis mediator. Ten OBPs (MmedOBP11–20) and two CSPs (MmedCSP2–3) were newly identified. The expression patterns of these new genes in olfactory and non-olfactory tissues were investigated by real-time quantitative PCR (qPCR) measurement. The results indicated that MmedOBP14, MmedOBP18, MmedCSP2 and MmedCSP3 were primarily expressed in antennae suggesting potential olfactory roles in M. mediator. However, other genes including MmedOBP11–13, 15–17, 19–20 appeared to be expressed at higher levels in body parts than in antennae. Focusing on the functional characterization of MmedCSP3, immunocytochemistry and fluorescent competitive binding assays were conducted indoors. It was found that MmedCSP3 was specifically located in the sensillum lymph of olfactory sensilla basiconca type 2. The recombinant MmedCSP3 could bind several types of host insects odors and plant volatiles. Interestingly, three sex pheromone components of Noctuidae insects, cis-11-hexadecenyl aldehyde (Z11-16: Ald), cis-11-hexadecanol (Z11-16: OH), and trans-11-tetradecenyl acetate (E11-14: Ac), showed high binding affinities (Ki = 17.24–18.77 μM). The MmedCSP3 may be involved in locating host insects. Our data provide a base for further investigating the physiological roles of OBPs and CSPs in M. mediator, and extend the function of MmedCSP3 in chemoreception of M. mediator.
In insects, behaviors of host identification, mating-partners, and locating oviposition sites are regulated largely by volatile chemical cues [1, 2]. These odor molecules are usually perceived by chemosensory sensilla located on their antennae . In insect olfaction model, odorants enter the chemosensory sensilla through cuticular pores, dissolved in the sensillum lymph and are captured by soluble carrier proteins, then activate sensory neurons [4, 5]. Two major classes of soluble proteins, odorant binding proteins (OBPs) and chemosensory proteins (CSPs) play essential roles in transferring semiochemicals to the membrane-bonded receptors, and may contribute to the activation of olfactory receptor neurons [6, 7].
In the present study, we obtained 20 OBPs and 3 CSPs from the antennal transcriptome of M. mediator, among them 10 OBPs and 2 CSPs were newly reported. There are 52 OBPs and 4 CSPs identified in Drosophila melanogaster , 45 OBPs and 16 CSPs in Bombyx mori , while Apis mellifera has 21 OBPs and 6 CSPs [15, 27], C. cunea has 25 OBPs and 11 CSPs . The total number of OBPs and CSPs in M. mediator is smaller than in D. melanogaster and B. mori, but similar to those in A. mellifera and C. cunea. We suspected that there was less OBPs and CSPs in Hymenoptera insects. Of course, some potential OBPs and CSPs may not able to be identified in M. mediator due to low expressions level in the antennae or specific expression in other tissues.