A transposon-introduced G-quadruplex motif is selectively retained and constrained to downregulate CYP321A1

Authors: DENG, ZHONGYUAN - Zhengzhou University; ZHANG, YUTING - Zhengzhou University; GAO, CHAO - Huazhong Agricultural University; SHEN, WEI - Huazhong Agricultural University; WANG, SHAN - Zhengzhou University; Ni, Xinzhi; LIU, SISI - Huazhong Agricultural University; LI, XIANCHUN - University Of Arizona

Submitted to: Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2022
Publication Date: 12/1/2022
Citation: Deng, Z., Zhang, Y., Gao, C., Shen, W., Wang, S., Ni, X., Liu, S., Li, X. 2022. A transposon-introduced G-quadruplex motif is selectively retained and constrained to downregulate CYP321A1. Insect Science. 29(6):1629-1642. https://doi.org/10.1111/1744-7917.13021.
DOI: https://doi.org/10.1111/1744-7917.13021

Interpretive Summary: Cytochrome P450 monooxygenases (P450s) is a diverse class of detoxification enzymes found in all animals including insects. They play important roles in metabolism and detoxification of xenobiotics including toxic phytochemicals and synthetic insecticides. To cope with the uncertainty and unpredictability of plant defense allelochemicals and insecticides, herbivorous insects have evolved a flexible regulatory system. At least seven signaling pathways have been implicated in xenobiotic induction of P450s. However, little is known about the silencers, transcription suppressor/co-suppressors, and the upstream effectors of the signaling pathways that suppress the expression of xenobiotic-metabolizing P450s. It remains unclear whether and how P450s of any species acquire and retain transposon-introduced G-quadruplex motif (or in short, G4 motifs) to adjust their expression in response to xenobiotic signals. In the current study, we chose a xenobiotic-metabolizing P450 gene (CYP321A1) from the corn earworm as a representative of P450 genes to address the general question of whether and how the P450 genes obtain and keep G4 motifs to mediate their expression and to fill the knowledge gap in the silencer-mediated down-regulation of P450 genes. We demonstrated that transposon-inserted P450 genes and the transposon-introduced G4 motifs were selectively retained and constrained in the field populations of the corn earworm. This represents the first report of the cytochrome P450 gene recruitment and retention of G4 motifs via transposons to regulate their expression. The findings from this study have broad impact on understanding insecticide and transgenic insecticidal protein resistance in the corn earworm and other polyphagous lepidopteran insect pests in short term, which would lead to developing new innovative pest management strategies in long term.

Technical Abstract: Insects utilize xenobiotic compounds to up- and down-regulate cytochrome P450 monooxygenases (P450s) involved in detoxification of toxic xenobiotics including phytochemicals and pesticides. G-quadruplexes (G4)-forming DNA motifs are enriched in the promoter regions of transcription factors and function as cis-acting elements to regulate these genes. Whether and how P450s gain and keep G4 DNA motifs to regulate their expression still remain unexplored. Here, we show that CYP321A1, a xenobiotic-metabolizing P450 from Helicoverpa zea, a polyphagous insect of economic importance, has acquired and preserved a G4 DNA motif by selectively retaining a transposon known as HzIS1-3 that carries this G4 DNA motif in its promoter region. The HzIS1-3 G4 DNA motif acts as a silencer to suppress the constitutive and induced expression of CYP321A1 by plant allelochemicals flavone and xanthotoxin through folding into an intramolecular parallel or hybrid-1 conformation in the absence or presence of K+. The G4 ligand N-methylmesoporphyrin IX (NMM) strengthens the silencing effect of HzIS1-3 G4 DNA motif by switch its structure from hybrid-1 to hybrid-2. The enrichment of transposons in P450s and other environment-adaptation genes implies that selective retention of G4 DNA motif-carrying transposons may be the main evolutionary route for these genes to obtain G4 DNA motifs.