Gene-Guided Discovery and Ribosomal Biosynthesis of MoroidinPeptides

Moroidin is a bicyclic plant octapeptide withtryptophan side-chain cross-links, originally isolated as a pain-causing agent from the Australian stinging treeDendrocnidemoroides. Moroidin and its analog celogentin C, derived fromCelosia argentea, are inhibitors of tubulin polymerization and, thus,lead structures for cancer therapy. However, low isolation yieldsfrom source plants and challenging organic synthesis hindermoroidin-based drug development. Here, we present biosynthesisas an alternative route to moroidin-type bicyclic peptides andreport that they are ribosomally synthesized and posttranslationallymodified peptides (RiPPs) derived from BURP-domain peptidecyclases in plants. By mining 793 plant transcriptomes formoroidin core peptide motifs within BURP-domain precursorpeptides, we identified a moroidin cyclase in Japanese kerria, which catalyzes the installation of the tryptophan-indole-centeredmacrocyclic bonds of the moroidin bicyclic motif in the presence of cupric ions. Based on the kerria moroidin cyclase, wedemonstrate the feasibility of producing diverse moroidins including celogentin C in transgenic tobacco plants and report specificcytotoxicity of celogentin C against a lung adenocarcinoma cancer cell line. Our study sets the stage for future biosyntheticdevelopment of moroidin-based therapeutics and highlights that mining plant transcriptomes can reveal bioactive cyclic peptides andtheir underlying cyclases from new source plants.