Transcript-Level Analysis in Combination with Real-Time PCR Elucidates Heat Adaptation Mechanism of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) Larvae

Trehalose 6-phosphate synthase gene rdtps1 contributes to thermal acclimation in Rhyzopertha dominica

BACKGROUND

The lesser grain borer (Rhyzopertha dominica), a worldwide primary pest of stored grain, causes serious economic losses and threatens stored food safety. R. dominica can respond to changes in temperature, especially the adaptability to heat. In this study, transcriptome analysis of R. dominica exposed to different temperatures was performed to elucidate differences in gene expression and the underling molecular mechanism.

RESULTS

Isoform-sequencing generated 17,721,200 raw reads and yielded 20,416 full-length transcripts. A total of 18,880 (92.48%) transcripts were annotated. We extracted RNA from R. dominica reared at 5 °C (cold stress), 15 °C (cold stress), 27 °C (ambient temperature) and 40 °C (heat stress) for RNA-seq. Compared to those of control insects reared at 27 °C, 119, 342, and 875 differentially expressed genes (DEGs) were identified at 5 °C, 15 °C, and 40 °C, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that pathways associated with "fatty acid metabolism", "fatty acid biosynthesis", "AMPK signaling pathway", "neuroactive ligand receptor interaction", and "longevity regulating pathway-multiple species" were significantly enriched. The functional annotation revealed that the genes encoding heat shock proteins (HSPs), fatty acid synthase (FAS), phospholipases (PLA), trehalose transporter (TPST), trehalose 6-phosphate synthase (TPS), and vitellogenin (Vg) were most likely involved in temperature regulation, which was also validated by RT-qPCR. Seven candidate genes (rdhsp1, rdfas1, rdpla1, rdtpst1, rdtps1, rdvg1, and rdP450) were silenced in the RNA interference (RNAi) assay. RNAi of each candidate gene suggested that inhibiting rdtps1 expression significantly decreased the trehalose level and survival rate of R. dominica at 40 °C.

CONCLUSIONS

These results indicated that trehalose contributes to the high temperature resistance of R. dominica. Our study elucidates the molecular mechanisms underlying heat tolerance and provides a potential target for the pest management in R. dominica.

Comparative transcriptome analysis of Callosobruchus chinensis (L.) (Coleoptera: Chrysomelidae-Bruchinae) after heat and cold stress exposure

Callosobruchus chinensis is regarded as one of the cosmopolitan pests of legume crops and can cause tremendous losses to a variety of beans. This study focused on comparative transcriptome analyses of C. chinensis exposed to 45 °C (heat stress), 27 °C (ambient temperature) and -3 °C (cold stress) for 3 h to investigate the gene differences and underlying molecular mechanisms. There were 402 and 111 differentially expressed genes (DEGs) identified in the heat and cold stress treatments, respectively. "cell process", "cell" and "binding" were the main enriched functions and biological processes revealed by gene ontology (GO) analysis. The clusters of orthologous genes (COG) showed that DEGs were assigned to the categories: "posttranslational modification, protein turnover, chaperones", "lipid transport and metabolism", and "general function prediction only". With respect to the Kyoto Encyclopedia of Genes and Genomes (KEGG), the "longevity regulating pathway-multiple species", "carbon metabolism", "peroxisome", "protein processing in endoplasmic", "glyoxylate and dicarboxylate metabolism" pathways were significantly enriched. The annotation and enrichment analysis revealed that genes encoding heat shock proteins (Hsps) and cuticular proteins were significantly upregulated under high and low-temperature stresses, respectively. In addition, some DEGs encoding "Protein lethal essential for life", "Reverse transcriptase", "DnaJ domain", "Cytochrome" and "Zinc finger protein" were also upregulated to varying degrees. Transcriptomic data were validated using qRT‒PCR, which confirmed that they were consistent. In this paper, the temperature tolerance of C. chinensis adults was evaluated and the results showed that female adults were more sensitive to heat and cold stress than males, and the upregulation of heat shock protein and epidermal protein was the largest in DEGs after heat and cold stress, respectively. These findings provide a reference for further understanding the biological characteristics of C. chinensis adults and the molecular mechanisms underlying the response to low and high temperatures.