Identification and Characterization of Glutathione S-transferase Genes in Spodoptera frugiperda (Lepidoptera: Noctuidae) under Insecticides Stress

Abstract

Insect glutathione S-transferases (GSTs) serve critical roles in insecticides and other forms of xenobiotic chemical detoxification. The fall armyworm, Spodoptera frugiperda (J. E. Smith), is a major agricultural pest in several countries, especially Egypt. This is the first study to identify and characterize GST genes in S. frugiperda under insecticidal stress. The present work evaluated the toxicity of emamectin benzoate (EBZ) and chlorantraniliprole (CHP) against the third-instar larvae of S. frugiperda using the leaf disk method. The LC₅₀ values of EBZ and CHP were 0.029 and 1.250 mg/L after 24 h of exposure. Moreover, we identified 31 GST genes, including 28 cytosolic and 3 microsomal SfGSTs from a transcriptome analysis and the genome data of S. frugiperda. Depending on the phylogenetic analysis, sfGSTs were divided into six classes (delta, epsilon, omega, sigma, theta, and microsomal). Furthermore, we investigated the mRNA levels of 28 GST genes using qRT-PCR under EBZ and CHP stress in the third-instar larvae of S. frugiperda. Interestingly, SfGSTe10 and SfGSTe13 stood out with the highest expression after the EBZ and CHP treatments. Finally, a molecular docking model was constructed between EBZ and CHP using the most upregulated genes (SfGSTe10 and SfGSTe13) and the least upregulated genes (SfGSTs1 and SfGSTe2) of S. frugiperda larvae. The molecular docking study showed EBZ and CHP have a high binding affinity with SfGSTe10, with docking energy values of -24.41 and -26.72 kcal/mol, respectively, and sfGSTe13, with docking energy values of -26.85 and -26.78 kcal/mol, respectively. Our findings are important for understanding the role of GSTs in S. frugiperda regarding detoxification processes for EBZ and CHP.

Keywords: gene expression; glutathione S-transferase; insecticides; molecular docking; phylogenic tree.

Figure 1

Phylogenetic analysis of SfGSTs in S. frugiperda. The phylogenetic tree was constructed using a neighbor-joining method to analyze the amino acid sequences of insect GSTs. Sl, Spodoptera litura; Pr, Pieris rapae; Bm, Bombyx mori; Nl, Nilaparvata lugens; Sf, Sogatella furcifera; Dm, Drosophila melanogaster; Ld, Leptinotarsa decemlineata; Ap, Acyrthosiphon pisum.

Figure 2

Relative expression levels of SfGSTs in larvae exposed to an LC₅₀ of emamectin benzoate (EBZ) and chlorantraniliprole (CHP). Dunnett’s tests were performed to compare the gene expression of the tested insecticides with the corresponding control group (* p < 0.05, ** p < 0.01, *** p < 0.001).

Figure 2

Relative expression levels of SfGSTs in larvae exposed to an LC₅₀ of emamectin benzoate (EBZ) and chlorantraniliprole (CHP). Dunnett’s tests were performed to compare the gene expression of the tested insecticides with the corresponding control group (* p < 0.05, ** p < 0.01, *** p < 0.001).

Figure 3

Docking view of the binding interactions of emamectin benzoate (EBZ) within four receptors, (A) SfGSTe10, (B) SfGSTe13, (C) SfGSTs1, (D) SfGSTe2), in S. frugiperda. Left: two-dimensional interaction diagram of insecticide–receptor complexes. Right: the 3D complex structure and ligand bonds are depicted by yellow lines.

Figure 4

Docking view of the binding interactions of chlorantraniliprole (CHP) within four receptors, (A) SfGSTe10, (B) SfGSTe13, (C) SfGSTs1, (D) SfGSTe2), in S. frugiperda. Left: two-dimensional interaction diagram of insecticide–receptor complexes. Right: the 3D complex structure and ligand bonds are depicted by yellow lines.