Guo Bing, Hao Enhua, Qiao Haili, Wang Jingzhen, Wu Weiwei, Zhou Jingjiang, Lu Pengfei
The Key Laboratory for Silviculture and Conservation of the Ministry of Education, School of Forestry, Beijing Forestry University, 35 Qinghua Dong Road, Haidian District, Beijing, 100083, People's Republic of China.
Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100193, People's Republic of China.
BMC Genomics. 2021 Mar 10;22(1):172. doi: 10.1186/s12864-021-07452-1.
The woodwasp Sirex noctilio Fabricius is a major quarantine pest worldwide that was first discovered in China in 2013 and mainly harms Pinus sylvestris var. mongolica Litv.. S. nitobei Matsumura is a native species in China and is closely related to S. noctilio. Recently, the two woodwasps species were found attacking the P. sylvestris var. mongolica Litv in succession. The olfactory system is the foundation of insect behavior. Olfactory genes were identified through antennal transcriptome analysis. The expression profiles odorant binding proteins (OBPs) were analyzed with RT-qPCR.
From our transcriptome analysis, 16 OBPs, 7 chemosensory proteins (CSPs), 41 odorant receptors (ORs), 8 gustatory receptors (GRs), 13 ionotropic receptors (IRs), and one sensory neuron membrane protein (SNMP) were identified in S. noctilio, while 15 OBPs, 6 CSPs, 43 ORs, 10 GRs, 16 IRs, and 1 SNMP were identified in S. nitobei. Most of the olfactory genes identified in two species were homologous. However, some species-specific olfactory genes were identified from the antennal transcriptomes, including SnocOBP13, SnocCSP6, SnocOR26, SnocGR2, SnocIR7 in S. noctilio and SnitGR9, SnitGR11, SnitIR17 in S. nitobei. In total, 14 OBPs were expressed primarily in the antennae. SnocOBP9 and SnitOBP9, identified as PBP homologues, were sex-biased expression in two siricid, but with different pattern. SnocOBP11 and SnitOBP11 were highly expressed in antennae and clearly expressed in external genitalia. SnocOBP7 and SnitOBP7 were highly expressed in male genitalia. SnocOBP3 and SnocOBP10 were highly expressed in female genitalia and male heads, while SnitOBP3 and SnitOBP10 did not show obvious tissue bias.
We analyzed 86 and 91 olfactory genes from S. noctilio and S. nitobei, respectively. Most of the olfactory genes identified were homologous, but also some species-specific olfactory genes were identified, which indicated the similarities and differences of the molecular mechanisms between the two closely-related species. Different expression in the antennae, external genitals or heads, exhibiting an obvious sex bias, suggested their different role in recognizing sex pheromones or plant volatiles. Species-specific expression for several OBPs genes may suggest that they strengthened or lost their original function during species differentiation, resulting in olfactory differences between the two species.
木蜂树蜂（Sirex noctilio Fabricius）是一种全球主要检疫性害虫，2013年首次在中国被发现，主要危害樟子松（Pinus sylvestris var. mongolica Litv.）。日本树蜂（S. nitobei Matsumura）是中国本土物种，与木蜂树蜂密切相关。最近，发现这两种树蜂先后攻击樟子松。嗅觉系统是昆虫行为的基础。通过触角转录组分析鉴定嗅觉基因。用RT-qPCR分析气味结合蛋白（OBP）的表达谱。
通过转录组分析，在木蜂树蜂中鉴定出16种OBP、7种化学感受蛋白（CSP）、41种气味受体（OR）、8种味觉受体（GR）、13种离子otropic受体（IR）和1种感觉神经元膜蛋白（SNMP），而在日本树蜂中鉴定出15种OBP、6种CSP、43种OR、10种GR、16种IR和1种SNMP。两个物种中鉴定出的大多数嗅觉基因是同源的。然而，从触角转录组中鉴定出了一些物种特异性嗅觉基因，包括木蜂树蜂中的SnocOBP13、SnocCSP6、SnocOR26、SnocGR2、SnocIR7和日本树蜂中的SnitGR9、SnitGR11、SnitIR17。总共14种OBP主要在触角中表达。被鉴定为PBPs同源物的SnocOBP9和SnitOBP9在两种树蜂中存在性别偏向表达，但模式不同。SnocOBP11和SnitOBP11在触角中高表达，在生殖器中明显表达。SnocOBP7和SnitOBP7在雄性生殖器中高表达。SnocOBP3和SnocOBP10在雌性生殖器和雄性头部中高表达，而SnitOBP3和SnitOBP10没有明显的组织偏向性。
我们分别分析了木蜂树蜂和日本树蜂的86个和91个嗅觉基因。鉴定出的大多数嗅觉基因是同源的，但也鉴定出了一些物种特异性嗅觉基因，这表明这两个密切相关物种之间分子机制的异同。在触角、外生殖器或头部的不同表达，表现出明显的性别偏向，表明它们在识别性信息素或植物挥发物方面的不同作用。几个OBP基因的物种特异性表达可能表明它们在物种分化过程中增强或丧失了原始功能，导致两个物种之间的嗅觉差异。
