Identification of the Flavone-Inducible Counter-Defense Genes and Their cis-Elements in Helicoverpa armigera

Flavone is widely found in plants and plays an important role in plant defense against pests. Many pests, such asHelicoverpa armigera, use flavone as a cue to upregulate counter-defense genes for detoxification of flavone. Yet the spectrum of the flavone-inducible genes and their linkedcis-regulatory elements remains unclear. In this study, 48 differentially expressed genes (DEGs) were found by RNA-seq. These DEGs were mainly concentrated in the retinol metabolism and drug metabolism-cytochrome P450 pathways. Further in silico analysis of the promoter regions of 24 upregulated genes predicted two motifs through MEME and five previously characterizedcis-elements including CRE, TRE, EcRE, XRE-AhR and ARE. Functional analysis of the two predicted motifs and two different versions of ARE (named ARE1 and ARE2) in the promoter region of the flavone-inducible carboxylesterase geneCCE001jverified that the two motifs and ARE2 are not responsible for flavone induction ofH. armigeracounter-defense genes, whereas ARE1 is a new xenobiotic response element to flavone (XRE-Fla) and plays a decisive role in flavone induction ofCCE001j. This study is of great significance for further understanding the antagonistic interaction between plants and herbivorous insects.Keywords:Helicoverpa armigera;flavone;detoxification metabolism;carboxylesterase;cis-transcriptional regulation;AREKey Contribution:The spectrum of flavone up- and downregulated genes was revealed by transcriptomic analysis of the midgut of cotton bollworm treated with flavone, and an ARE-likecis-acting element in the promoter ofCCE001jwas found to determine whether the gene was induced by flavone.