Insecticidal activity and underlying molecular mechanisms of a phytochemical plumbagin against Spodoptera frugiperda

Abstract

Introduction: Plumbagin is an important phytochemical and has been reported to exhibit potent larvicidal activity against several insect pests, However, the insecticidal mechanism of plumbagin against pests is still poorly understood. This study aimed to investigate the insecticidal activities of plumbagin and the underlying molecular mechanisms against a devastating agricultural pest, the fall armyworm Spodoptera frugiperda.

Methods: The effects of plumbagin on S. frugiperda larval development and the activities of two detoxification enzymes were initially examined. Next, transcriptomic changes in S. frugiperda after plumbagin treatment were investigated. Furthermore, RNA-seq results were validated by qPCR.

Results: Plumbagin exhibited a high larvicidal activity against the second and third instar larvae of S. frugiperda with 72 h LC₅₀ of 0.573 and 2.676 mg/g, respectively. The activities of the two detoxification enzymes carboxylesterase and P450 were significantly increased after 1.5 mg/g plumbagin treatment. Furthermore, RNA-seq analysis provided a comprehensive overview of complex transcriptomic changes in S. frugiperda larvae in response to 1.5 mg/g plumbagin exposure, and revealed that plumbagin treatment led to aberrant expression of a large number of genes related to nutrient and energy metabolism, humoral immune response, insect cuticle protein, chitin-binding proteins, chitin synthesis and degradation, insect hormone, and xenobiotic detoxification. The qPCR results further validated the reproducibility and reliability of the transcriptomic data.

Discussion: Our findings provide a valuable insight into understanding the insecticidal mechanism of the phytochemical plumbagin.

Keywords: RNA-seq; Spodoptera frugiperda; detoxification enzyme; plumbagin; toxicological mechanism.

FIGURE 1

The survival rate (A) and larval weight (B) of S. frugiperda after 1.5 mg/g plumbagin treatment.

FIGURE 2

The activities of two detoxification enzymes in third-instar S. frugiperda larvae after 1.5 mg/g plumbagin treatment. (A) Carboxylesterase (CarE) activity. (B) P450 activity.

FIGURE 3

Transcriptome profile of RNA-Seq data. (A) Correlation matrix of the samples utilizing Spearman’s correlation coefficients. (B) Principal component analysis of the samples. (C) Volcano plot of RNA-Seq data.

FIGURE 4

Enrichment analyses of differentially expressed genes (DEGs) in S. frugiperda larvae after 1.5 mg/g plumbagin treatment.

FIGURE 5

Heatmap analysis of differentially expressed genes (DEGs) in S. frugiperda larvae after plumbagin treatment. CLIP, clip domain serine protease; SOCS, suppressor of cytokine signaling 2; PGRPs, peptidoglycan recognition proteins; CHMP7, charged multivesicular body protein 7; HSPA1_6_8, heat shock 70 kDa protein 1/2/6/8; SMAP, stromal membrane-associated protein; VPS35, vacuolar protein sorting-associated protein 35; EPS15, epidermal growth factor receptor substrate 15; JHEH, juvenile hormone epoxide hydrolase; JHBP, haemolymph juvenile hormone binding protein; PRKAG, 5′-AMP-activated protein kinase, regulatory gamma subunit; FASN, fatty acid synthase, animal type; SREBF1, sterol regulatory element-binding transcription factor 1; PPP1R3, protein phosphatase 1 regulatory subunit 3A/B/C/D/E; SLC2A1, solute carrier family 2 (facilitated glucose transporter), member 1; HSPA5, heat shock 70 kDa protein 5; SLC16A10, solute carrier family 16 (monocarboxylic acid transporters), member 10; PLCE, phosphatidylinositol phospholipase C, epsilon; CYP15A1_C1, methyl farnesoate epoxidase/farnesoate epoxidase; WASH1, WAS protein family homolog 1.

FIGURE 6

Comparison of expression levels of selected genes in RNA-seq and qPCR.