Structure-function analysis of MhieJHAMT: a key enzyme in Monolepta hieroglyphica juvenile hormone biosynthesis

Monolepta hieroglyphica, a major pest of Chinese crops, demands effective control. Targeting juvenile hormone acid O-methyltransferase, a key enzyme in JH production, presents a promising strategy for developing novel, specific insecticides. This study investigated the structure-function of M. hieroglyphica juvenile hormone acid O-methyltransferase (MhieJHAMT), a key enzyme in the JH pathway. Phylogenetic analysis showed MhieJHAMT's conservation within Coleoptera, suggesting a conserved catalytic mechanism. In vitro enzymatic activity assays confirmed MhieJHAMT's catalytic function. Bioinformatics (molecular dynamics and docking) revealed 19 amino acid residues forming the active site, binding S-adenosylmethionine (SAM) and farnesoic acid (FA). In vivo RNA interference (RNAi) coupled with ELISA demonstrated MhieJHAMT's crucial role in JH biosynthesis; its knockdown significantly reduced JH titers. Quantitative real-time PCR (RT-qPCR) revealed higher MhieJHAMT expression in female intestines and gonads, hinting at additional functions beyond JH biosynthesis. Interestingly, our findings reveal an intriguing correlation between host plant-mediated alterations in farnesyl pyrophosphate synthase 1 (MhieFPPS1) expression and that of MhieJHAMT, with MhieFPPS1 appearing to function upstream of MhieJHAMT. The observation suggests a potential positive feedback loop, hinting at a complex regulatory mechanism. This comprehensive study elucidates MhieJHAMT's function, its regulatory mechanisms, and its potential as a novel pest control target.