Transcriptional Response of ATP-Binding Cassette (ABC) Transporters to Insecticide in the Brown Planthopper, Nilaparvata lugens (Stål)

Abstract

The ATP-binding cassette (ABC) transporter superfamily is one of the largest groups of proteins and plays a non-negligible role in phase III of the detoxification process, which is highly involved in the response of insects to environmental stress (plant secondary metabolites and insecticides). In the present study, in Nilaparvata lugens, we identified 32 ABC transporters, which are grouped into eight subfamilies (ABCA-H) based on phylogenetic analysis. The temporal and spatial expression profiles suggested that the nymphal stages (1st-5th) and adult males showed similarity, which was different from eggs and adult females, and NlABCA1, NlABCA2, NlABCB6, NlABCD2, NlABCG4, NlABCG12, NlABCG15, and NlABCH1 were highly expressed in the midgut and Malpighian tubules. In addition, ABCG12, which belongs to the ABC transporter G subfamily, was significantly upregulated after exposure to sulfoxaflor, nitenpyram, clothianidin, etofenprox, chlorpyrifos, and isoprocarb. Moreover, verapamil significantly increased the sensitivity of N. lugens to nitenpyram, clothianidin, etofenprox, chlorpyrifos, and isoprocarb. These results provide a basis for further research on ABC transporters involved in detoxification in N. lugens, and for a more comprehensive understanding of the response of N. lugens to environmental stress.

Keywords: ABC transporters; Nilaparvata lugens; detoxification; insecticides.

Figure 1

Phylogenetic tree of the Nilaparvata lugens ATP-binding cassette (ABC) transporters. Amino acid sequences of nucleotide-binding domains (NBDs) from N. lugens (Nl) and Laodelphax striatellus (Ls) were aligned using ClustalW and analyzed by the maximum likelihood method in MEGA7 [39]. The bootstrap consensus tree, inferred from 1000 replicates, is taken to represent the evolutionary history of the taxa analyzed. The bootstrap values are shown on the branches. Each color represents one ABC subfamily: A–H.

Figure 2

Relative expression levels of ABC transporters at different developmental stages in the N. lugens life cycle, as determined by qRT-PCR. Letters on the right are the gene names for the 32 ABC transporters. Developmental stages are given at the bottom. The mRNA levels, represented by normalized log10 (∆CT) values, are shown in the gradient heatmap. The color from light to dark indicates the expression level from low to high.

Figure 3

Relative expression levels of ABC transporters in different tissues of 5th instar N. lugens, as determined by qRT-PCR. Letters on the right are the gene names for the 32 ABC transporters. Tissue types are given at the bottom; MT, Malpighian tubules. The mRNA levels, represented by normalized log10 (∆CT) values, are shown in the gradient heatmap. The color from light to dark indicates the expression level from low to high.

Figure 4

Relative expression levels of 32 ABC transporters in N. lugens nymphs treated with insecticides, as determined by qRT-PCR. Letters on the right are the gene names for the 32 ABC transporters. Treatments are given at the bottom. The mRNA levels were normalized by the expression of the respective gene in untreated nymphs. Blue indicates downregulated, and red indicates upregulated. The more intense the color, the more pronounced are the changes in expression levels.

Figure 5

Summary of genes that were significantly upregulated after exposure to different insecticides. The link indicates that the gene was significantly upregulated after insecticide induction. The orange line indicates the genes that are upregulated after induction by three neonicotinoid insecticides. The purple line indicates genes that are upregulated after induction of six insecticides (p < 0.05).