In the warfare between herbivore and host plant, insects have evolved a variety of defensive mechanisms, including allelochemical transformation and excretion. Several studies have explored the transcriptome responses of insects after host plant shifts to understand these mechanisms. We investigated the plastic responses of Heliconius melpomene larvae feeding on a native host Passiflora menispermifolia and a less strongly defended nonhost species, Passiflora biflora. In total, 326 differentially expressed genes were identified, with a greater number upregulated on the more strongly defended native host. Functional annotation showed that detoxifying enzymes, transporters and components of peritrophic membrane were strongly represented. In total, 30 candidate detoxification genes were differentially expressed, with glutathione S-transferases (GSTs) and UDP-glucuronosyltransferases (UGTs) showing the highest proportion of differential expression, 27.3% and 17.3%, respectively. These differentially expressed detoxification genes were shown to evolve mainly under the influence of purifying selection, suggesting that protein-coding evolution has not played a major role in host adaptation. We found only one gene, GSTe3, with evidence of adaptive evolution at H40, which is around the G-site and might alter enzyme activity. Based on our transcriptome and molecular evolution analysis, we suggest that transcriptional plasticity of genes in a herbivore may play an important role in adaptation to a new host plant.
Fig. S1 Gene ontology classification of the postman butterfly genes expressed in the gut.
GEG: gene expressed in the gut. GHG: gene highly expressed in the gut.
Fig. S1.pdf
Fig. S2 Scatterplot of enriched pathways for DEGs in larval gut after host plant shift.
The size and color of the dots represent the gene number and the range of the FDR value, respectively. Rich factor is the ratio of the differentially expressed gene number to the total gene number in a certain pathway. Four pathway databases were used in our analysis, including Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, Reactome, BioCyc and Protein Analysis Through Evolutionary Relationships (PANTHER).
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Fig. S3 NJ tree and intron positions of HmelGST genes.
Phase 0, 1, and 2 introns are shown by black, blue, and red solid lines, respectively.
Fig. S3.pdf
Fig. S4 Distributions of H. melpomene GST and UGT genes on chromosmes.
Scaffold arrangement is based on the published linkage map (Heliconius Genome Consortium 2012).
Fig. S4.pdf
Fig. S5 Duplication mechanisms and conserved motif of UGT33 family in H. melpomene.
MCScanX (max gaps = 50) was used to identify the segmental and tandem duplications of detoxification genes in H. melpomene. This annotated tree was predicted by the collinear and tandem relationships of the output from ‘family tree plotter of MCScanX’. The characters T and S on the nodes mean tandem and segmental duplications, respectively. All the UGT33 family members in Fig. 4 were used to create sequence logo of signature region (http://weblogo.berkeley.edu/logo.cgi).
Fig. S5.pdf
Fig. S6 Gene gain and loss of GSTs superfamily in Heliconius butterflies.
The species tree was derived from a phylogeny based on independent nuclear and mitochondrial DNA sequences (Beltran et al. 2007). Each class of GSTs from 10 Heliconius species were reconstructed the NJ phylogenectic tree. Gene gain and loss was estimated with the method of Nam & Nei (2005).
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Table S1 Primer sequences used for quantitative PCR validation.
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Table S2 Annotation and sequences of GST and UGT multigene families in H. melpomene and Danaus plexippus genome.
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Table S3 Sequences of detoxifying genes were used for PAML analysis.
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Table S4 Summary of reads and assembly of the gut transcriptomes in H. melpomene.
“host” and “non” represent the samples from individuals reared with host and non host plant, respectively. The number after the sample name means replicates.
Table S4.xlsx
Table S5 Annotations and expression signals of 326 DEGs in larval gut after host plant shift.
The protein sequences of all the genes were used as queries to Blastp search against nr database in NCBI (http://www.ncbi.nlm.nih.gov/). Transporter Classification DataBase (TCDB) was searched for the best hits of transporter genes (Saier et al. 2009). Peritrophin and genes related to nutrient digestion were classified by search against PFAM database (http://pfam.xfam.org/).
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Table S6 GO enrichment ananlysis of the differentially expressed genes.
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Table S7 Orthologous divergence of detoxification genes among Heliconius butterflies.
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Table S8 Differentially expressed genes detected by DESeq2 package
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