The role of bHLH transcription factor in the microbial stress response of Spodoptera litura

To determine relationships between the SlbHLH transcription factor (TF) and the microbial stress response in Spodoptera litura (Lepidoptera: Noctuidae), the SlbHLH binding sites in biopesticide-treated larvae were examined using DNA affinity purification sequencing (DAP-seq). A total of 3,004 genes were enriched near the gene transcription start site. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that SlbHLH binding target genes played roles in the stress and immune responses of S. litura. Weighted correlation network analysis (WGCNA) revealed expression trends of 67 target genes to be highly consistent with trends of SlbHLH, among which trends in target genes SlEPR1, SlHSF, SlOCT, and SlPCP36a were verified by real-time quantitative reverse transcription polymerase chain reaction. Yeast one-hybrid point-to-point verification and dual-luciferase reporter assays confirmed the existence of interactions between SlbHLH and SlPCP36a, as well as SlbHLH and SlEPR1. The sequence region TAGTTTC was identified as the binding site for both SlPCP36a and SlEPR1 to SlbHLH. These results provided a basis to identify correlations between SlbHLH TF and the response mechanism of microbial pesticide stress in S. litura.