A glutathione S‐transferase (BdGSTd9) participates in malathion resistance via directly depleting malathion and its toxic oxide malaoxon in Bactrocera dorsalis (Hendel)

Abstract

BACKGROUNDThe oriental fruit fly, Bactrocera dorsalis (Hendel), is a widespread agricultural pest that has evolved resistance to many commonly used insecticides including malathion. Glutathione S‐transferases (GSTs) are multifunctional enzymes that metabolize insecticides directly or indirectly. The specific mechanism used by GSTs to confer malathion resistance in B. dorsalis is unclear.RESULTSBdGSTd9 was identified from B. dorsalis and was expressed at twice the level in a malathion‐resistant strain (MR) than in a susceptible strain (MS). By using RNAi of BdGSTd9, the toxicity of malathion against MR was increased. Protein modelling and docking of BdGSTd9 with malathion and malaoxon indicated key amino acid residues for direct binding in the active site. In vitro assays with engineered Sf9 cells overexpressing BdGSTd9 demonstrated lower cytotoxicity of malathion. High performance liquid chromatography (HPLC) analysis indicated that malathion could be broken down significantly by BdGSTd9, and it also could deplete the malathion metabolite malaoxon, which possesses a higher toxicity to B. dorsalis. Taken together, the BdGSTd9 of B. dorsalis could not only deplete malathion, but also react with malaoxon and therefore enhance malathion resistance.CONCLUSIONBdGSTd9 is a component of malathion resistance in B. dorsalis. It acts by depleting both malathion and malaoxon. © 2020 Society of Chemical Industry

Functional analysis of a carboxylesterase gene involved in beta‐cypermethrin and phoxim resistance in Plutella xylostella (L.)

“…To further understand the function of PxαE8 in multi‐resistance, expression of PxαE8 was knocked down in GD‐2019 by RNAi and its resistance to the five insecticides was tested. Post‐transcriptional gene silencing by RNAi is an effective tool to investigate the functions of individual genes, 41,42 and has been widely used to study the roles of detoxifying enzyme genes in insecticide resistance 43–46 . Repression of PxαE8 by RNAi reduced CarE activity and resistance to beta‐cypermethrin and phoxim, which gave further proof that overexpression of PxαE8 was involved in phoxim and beta‐cypermethrin resistance in P. xylostella .…”

Multi-insecticide resistant malaria vectors in the field remain susceptible to malathion, despite the presence of Ace1 point mutations

“…Although the well-characterised DDT-metabolising GSTE2 [ 76 , 77 ] was not among them, other GSTs might likewise catalyse the dehydrochlorination of DDT [ 78 , 79 ] or be otherwise involved in the detoxification of different insecticides. Interestingly, GSTs may confer resistance to OPs as recently demonstrated for three GSTs of the oriental fruit fly Bactrocera dorsalis that can deplete malathion and its highly toxic metabolite malaoxon [ 80 , 81 ]. Whether such a GST-mediated OP detoxification mechanism also exists in malaria vectors remains to be elucidated.…”

An odorant‐binding protein of Asian citrus psyllid, Diaphorina citri, participates in the response of host plant volatiles

“…ch/docking) based on the EADock DSS method. 35,36 Visual analysis of molecular docking results was undertaken using PyMOL Stereo 3D Zalman software.…”