Transcriptomic modulation in response to an intoxication with deltamethrin in a population of Triatoma infestans with low resistance to pyrethroids

Abstract

Background: Triatoma infestans is the main vector of Chagas disease in the Southern Cone. The resistance to pyrethroid insecticides developed by populations of this species impairs the effectiveness of vector control campaigns in wide regions of Argentina. The study of the global transcriptomic response to pyrethroid insecticides is important to deepen the knowledge about detoxification in triatomines.

Methodology and findings: We used RNA-Seq to explore the early transcriptomic response after intoxication with deltamethrin in a population of T. infestans which presents low resistance to pyrethroids. We were able to assemble a complete transcriptome of this vector and found evidence of differentially expressed genes belonging to diverse families such as chemosensory and odorant-binding proteins, ABC transporters and heat-shock proteins. Moreover, genes related to transcription and translation, energetic metabolism and cuticle rearrangements were also modulated. Finally, we characterized the repertoire of previously uncharacterized detoxification-related gene families in T. infestans and Rhodnius prolixus.

Conclusions and significance: Our work contributes to the understanding of the detoxification response in vectors of Chagas disease. Given the absence of an annotated genome from T. infestans, the analysis presented here constitutes a resource for molecular and physiological studies in this species. The results increase the knowledge on detoxification processes in vectors of Chagas disease, and provide relevant information to explore undescribed potential insecticide resistance mechanisms in populations of these insects.

Fig 1. Effect of deltamethrin treatment on the transcription of differentially expressed genes identified in T. infestans.

Heatmap was plotted using z-score calculated from the transformed count data, by means of a color scale in which blue/red represent lowest/highest expression. The dendrogram on the left represents the results of the row hierarchical clustering. A: Acetone (control) samples. D: Deltamethrin-treated samples.

Fig 2. Phylogenetic tree of the CSP family from T. infestans, T. brasiliensis and R. prolixus.

The maximum-likelihood tree was constructed using IQ-Tree and protein sequences obtained from the transcriptomes of T. infestans (Triin-, red, available in Table E in S2 File) and T. brasiliensis (Tribr-, black, obtained from [28], and from the R. prolixus genome (Rhopr-, blue, NTE: N-terminus missing in gap; FX: gene model repaired based on de novo transcriptome assemblies; obtained from [29]). Sequences from T. infestans were named according to their R. prolixus orthologues, with the exception of Triin-CSP20 and Triin-CSP21 which have no orthologues in R. prolixus. Branches with SH-aLRT support values > 80 are marked with a grey dot. The tree was rooted at midpoint.

Fig 3. Effect of deltamethrin on the transcription of T. infestans CSPs.

The heatmap was created using Transcript per Million (TPM) as input of the gplot R package. Transcript abundance was represented as Log₁₀(TPM +1) where white/red represents the lowest/highest expression. A dendrogram was plotted using a hierarchical clustering of gene expression values based on Euclidean distance and complete linkage method for clustering. A: Acetone (control) samples. D: Deltamethrin-treated samples. Expression data of T. infestans CSP3, CSP18 and CSP22 is not available because these sequences were obtained from [5] and they were not detected in the transcriptome generated in this work.

Fig 4. Phylogenetic tree of the HSP70 superfamily from T. infestans, R. prolixus and D. melanogaster.

The maximum-likelihood tree was constructed using IQ-Tree and protein sequences obtained from T. infestans transcriptome (Triin-, red, available in Table F in S2 File) and from R. prolixus (RPRC-, blue, VectorBase ID is shown) and D. melanogaster (Drome-, green, FlyBase gene name and isoform are shown) genomes. Rhodnius prolixus chimeric sequence and those shorter than 250 amino acids were excluded from the analysis (Table F in S2 File). Triatoma infestans sequences were numbered according to their position in the tree. Branches with SH-aLRT support values > 80 are marked with a grey dot. The tree was rooted at midpoint.

Fig 5. Effect of deltamethrin on the transcription of the T. infestans HSP70 family.

The heatmap was created using Transcript per Million (TPM) as input of the gplot R package. Transcript abundance was represented as Log₁₀(TPM +1) where white/red represents the lowest/highest expression. A dendrogram was plotted using a hierarchical clustering of gene expression values based on Euclidean distance and complete linkage method for clustering. A: acetone (control) samples. D: deltamethrin-treated samples.

Fig 6. Phylogenetic tree of the ABC transporter superfamily from T. infestans, R. prolixus and D. melanogaster.

The maximum-likelihood tree was constructed using IQ-Tree and protein sequences obtained from T. infestans transcriptome (Triin-, red, available in Table G in S2 File) and from R. prolixus (RPRC-, blue, VectorBase ID is shown) and D. melanogaster (Drome-, green, FlyBase gene name and isoform are shown) genomes. Only those sequences complete enough for phylogenetic characterization were included in the tree (remaining sequences were given a preliminary classification shown in brackets in Table G in S2 File). Triatoma infestans sequences were numbered according to their position in the tree. Branches with SH-aLRT support values > 80 are marked with a grey dot. The tree was rooted at midpoint.

Fig 7. Effect of deltamethrin on the transcription of T. infestans ABC transporters.

The heatmap was created using Transcript per Million (TPM) as input of the gplot R package. Transcript abundance was represented as Log₁₀(TPM +1) where white/red represents the lowest/highest expression. A dendrogram was plotted using a hierarchical clustering of gene expression values based on Euclidean distance and complete linkage method for clustering. A: acetone (control) samples. D: deltamethrin-treated samples.