Nuclear receptors potentially regulate phytochemical detoxification in Spodoptera litura

Phytochemicals are a class of potential pesticides for pest control. Our previous studies have demonstrated that the development of Spodoptera litura is suppressed by two phytochemicals, flavone and xanthotoxin. Generally, phytochemical is metabolized by insect detoxification enzyme systems. Nuclear receptor (NR) is the ligand-activated transcription factor that involved in the regulation of detoxification gene expressions. To explore how NR responds to phytochemical to mediate detoxification gene expression, in the present study, 19 NRs were firstly identified in S. litura genome. The transcriptional levels of most NRs were significantly induced in the midgut of S. litura larvae after exposure to flavone and xanthotoxin. RNAi-mediated knockdown of FTZF1, EcR, Dsf, and HR3 remarkably reduced the larval tolerance to flavone or xanthotoxin. In addition, many crucial detoxification genes were downregulated by dsNR administrations, which might be responsible for the high sensitivity of S. litura to phytochemicals. Molecular docking indicated that phytochemicals as the potential ligands had high affinity to bind to NRs. This study suggested that NR potentially regulated the transcriptional expression of detoxification genes in response to phytochemical stresses, which partially elucidated the mechanism of extensive host adaptation in S. litura and provided the theoretical evidences for the development of NR-targeted insecticides.