Parallel evolution in the biosynthesis of a juvenile hormone compound reveals metabolic convergence in plants and insects

Plants have evolved diverse defenses against herbivores, and some species produce juvenile hormone III (JH III) that disrupts insect growth and reproduction. While the insect JH III biosynthetic pathway is well-established, its occurrence and basis in plants remain unresolved. We investigated the molecular and biochemical basis of JH III biosynthesis in the model sedge Cyperus iria. Comparative genomics, expression profiling, metabolic analyses, and in vitro enzyme assays were combined with transient pathway reconstruction in Nicotiana benthamiana. Cyperus iria harbors members of the same enzyme families of four insect JH III pathway enzymes but lacks a canonical farnesoic acid methyltransferase (FAMT). A pair of SABATH methyltransferases was identified as functional FAMTs (CiFAMT) in C. iria. Functional validation in N. benthamiana transient assay demonstrated that CiFAMT can replace the insect farnesoic acid methyltransferase within an otherwise insect-based pathway, confirming its role in methyl farnesoate biosynthesis. Our results demonstrate that plants and insects have independently evolved the capacity to biosynthesize structurally identical JH III through recruitment of non-homologous enzymes. This provides compelling evidence for structural convergent evolution of a specialized metabolite with ecological implications for plant-insect interactions.