Phytochemical Flavone Confers Broad-Spectrum Tolerance to Insecticides in Spodoptera litura by Activating ROS/CncC-Mediated Xenobiotic Detoxification Pathways

Abstract

Tolerance to chemical insecticides can be driven by the necessity of herbivorous insects to defend against host plantproduced phytochemicals. However, how the phytochemicals are sensed and further transduced into a defense response associated with insecticide tolerance is poorly understood. Herein, we show that pre-exposure to flavone, a flavonoid phytochemical, effectively enhanced larval tolerance to multiple synthetic insecticides and elevated detoxification enzyme activities in Spodoptera litura. RNA-Seq analysis revealed that flavone induced a spectrum of genes spanning phase I and II detoxification enzyme families, as well as two transcription factors Cap "n" collar isoform C (CncC) and its partner small muscle aponeurosis fibromatosis (MafK). Knocking down of CncC by RNA interference suppressed flavone-induced detoxification gene expression and rendered the larvae more sensitive to the insecticides. Flavone exposure elicited a reactive oxygen species (ROS) burst, while scavenging of ROS inhibited CncC-mediated detoxification gene expression and suppressed flavone-induced detoxification enzyme activation. Metabolome analysis showed that the ingested flavone was mainly converted into three flavonoid metabolites, and only 3-hydroxyflavone was found to affect the ROS/CncC pathway-mediated metabolic detoxification. These results indicate that the ROS/CncC pathway is an important route driving detoxification gene expression responsible for insecticide tolerance after exposure to the phytochemical flavone.

Activation of the ROS/CncC and 20-Hydroxyecdysone Signaling Pathways Is Associated with Xanthotoxin-Induced Tolerance to λ-Cyhalothrin in Spodoptera litura

“…Elevated P450 activity was found to be necessary for increased deltamethrin tolerance of H. armigera after exposure to gossypol, and the inducibility of P450 activity after quercetin ingestion was responsible for enhanced H. zea larval tolerance to λ-cyhalothrin. , Xanthotoxin-inducible detoxification enzymes with “broad-spectrum” characteristics are valuable to herbivorous insects to circumvent the adverse effects of environmental changes and increase their tolerance to insecticides. Similarly, we showed that dietary flavone exposure enhanced S. litura larval tolerance to different chemical classes of insecticides and activated multiple detoxification enzymes . The detoxification enzymes induced by various phytochemicals may help explain why this generalist species has quickly evolved tolerance to many synthetic insecticides …”

“…P450s, GSTs, UGTs, and CarEs are four insect detoxification enzyme superfamilies that metabolize both phytochemicals and synthetic insecticides. , Cheng et al sequenced the genome of S. litura and investigated the transcriptomic changes after exposure to xanthotoxin, ricin or imidacloprid by using RNA-Seq . The transcriptomic results showed that a fairly large number of detoxification genes were induced when larvae were exposed to xanthotoxin and that a great amount of them are also upregulated by flavone. , This indicates that the metabolic detoxification mechanisms of λ-cyhalothrin tolerance after xanthotoxin ingestion can be inferred from the study of flavone-induced detoxification genes. On the basis of these two RNA-Seq studies, , we selected 45 flavone-induced detoxification genes for qRT-PCR analysis.…”

“…Nevertheless, the mechanisms underlying the activation of the CncC in herbivorous insects are poorly understood, and further work is needed to test whether the induction of detoxification genes is due to phytochemical-induced nuclear translocation or upregulation of CncC. Research on the tobacco cutworm, Spodoptera litura , has demonstrated the role of ROS in initiating CncC and its partner MafK in response to flavone, a representative phytochemical of flavonoids . RNA-Seq analysis and functional validation revealed that ROS-dependent upregulation of CncC and MafK is responsible for the flavone induction of detoxification genes, and the ROS/CncC pathway was identified as the “master regulator” of the transcription of detoxification genes associated with the enhanced tolerance to insecticide in response to flavone .…”

“…Research on the tobacco cutworm, Spodoptera litura , has demonstrated the role of ROS in initiating CncC and its partner MafK in response to flavone, a representative phytochemical of flavonoids . RNA-Seq analysis and functional validation revealed that ROS-dependent upregulation of CncC and MafK is responsible for the flavone induction of detoxification genes, and the ROS/CncC pathway was identified as the “master regulator” of the transcription of detoxification genes associated with the enhanced tolerance to insecticide in response to flavone . A regulatory relationship between the ROS/CncC pathway and the downstream 20-hydroxy­ecdysone (20E) synthesis was observed in Bombyx mori .…”

Gut Microbiota Dysbiosis Influences Metabolic Homeostasis in Spodoptera frugiperda

“…Insects could reallocate resources when needed for survival; this makes it very difficult for pest control ( Poivet et al, 2021 ; Shu et al, 2021 ; Wang et al, 2021 ). Lipases and GSTs were significantly increased in the gut of S. litura after the antibiotic (streptomycin sulfate) treatment, implying that they might play key roles in improving the efficiency of conversion of ingested food to insect biomass and further resulted in faster development, which is responsible for antibiotics tolerance ( Thakur et al, 2016 ; Lu et al, 2021 ). Overall, our results were consistent with the previous studies that biological processes can be influenced by intestinal microbial population through transcriptional regulation.…”