Table_1_Characterization of Esterase Genes Involving Malathion Detoxification and Establishment of an RNA Interference Method in Liposcelis bostrychophila.doc

Esterases (ESTs) play important roles in metabolizing various physiologically endogenous and exogenous compounds, and various environmental xenobiotics in insects. The psocid, Liposcelis bostrychophila is a major pest of stored products worldwide and rapidly develops resistance to commonly insecticides. However, the involvement of ESTs in insecticide metabolization and the application of RNAi approach in psocids have not been well elucidated. In this study, we characterized four LbEST genes and investigated the transcriptional levels of these genes at different developmental stages and under different insecticides exposures to assess their potential roles in response to insecticides. The four LbESTs contain a catalytic triad (Ser-His-Glu) linked to an oxyanion hole and acyl pocket involved in substrate stabilization during its hydrolysis. Synergism observed with the esterase-inhibitor DEF suggests the involvement of esterases in malathion detoxification. LbESTs were expressed during the whole of developmental stages, but predominant abundance in the first nymphal instar and adult stage. The mRNA level of three LbEST genes (except for LbEST4) was induced (1.29- to 5.60 fold) in response to malathion or deltamethrin exposures, indicating that these esterases are involved in the detoxification process. Silencing of LbEST1, LbEST2 or LbEST3 through dsRNA feeding led to a higher mortality of psocids upon the malathion treatment compared to controls (1.83 to 2.69-fold), demonstrating that these esterase genes play roles in malathion detoxification in L. bostrychophila. Our study provides new evidence for understanding of the function and regulation mechanism of esterases in L. bostrychophila in insecticide detoxification. The current study also suggests that the present RNAi method could be applied for gene functional studies in psocids.

酯酶（Esterases）在昆虫体内可代谢多种生理内源性与外源性化合物，以及各类环境异生素，发挥关键生理功能。嗜卷书虱（Liposcelis bostrychophila）是全球范围内的主要储藏物害虫，且可快速对常用杀虫剂产生抗药性。然而，目前关于酯酶是否参与昆虫杀虫剂代谢，以及RNA干扰（RNAi）技术在书虱中的应用潜力，尚未得到充分阐明。本研究共鉴定得到4个LbEST基因，并检测了这些基因在不同发育阶段以及不同杀虫剂暴露处理下的转录水平，以评估其在杀虫剂响应过程中的潜在功能。这4个LbEST均包含与氧负离子孔相连的催化三联体（丝氨酸-组氨酸-谷氨酸），以及参与水解过程中底物稳定的酰基口袋。酯酶抑制剂DEF所介导的协同增效作用，提示酯酶参与了马拉硫磷的解毒过程。LbEST在所有发育阶段均有表达，但在1龄若虫与成虫阶段的表达量最为丰富。经马拉硫磷或溴氰菊酯暴露处理后，除LbEST4外的3个LbEST基因的mRNA水平均被诱导上调（上调幅度为1.29~5.60倍），表明这些酯酶参与了解毒代谢过程。通过饲喂双链RNA（dsRNA）沉默LbEST1、LbEST2或LbEST3后，嗜卷书虱在马拉硫磷处理下的死亡率较对照组升高1.83~2.69倍，证实这些酯酶基因在嗜卷书虱的马拉硫磷解毒过程中发挥重要功能。本研究为阐明嗜卷书虱酯酶在杀虫剂解毒中的功能与调控机制提供了新的实验证据，同时也表明RNAi技术可应用于书虱的基因功能研究。