Genome assembly of E lcysma westwoodi provides insights into host‐plant cyanogenic glucoside detoxification and chemical

Abstract

Elcysma westwoodi is a major pest of cherry trees (Rosaceae), which contain high levels of cyanogenic glucosides that release toxic hydrogen cyanide upon tissue damage. To investigate the genomic basis of host‐plant cyanogenic glucoside detoxification and the evolution of chemical defence genes, we generated a PacBio HiFi‐based genome assembly of E. westwoodi . The final assembly spans 460.62 Mb with high contiguity (contig N50 > 15 Mb) and near‐complete recovery of conserved genes (99.6% BUSCO completeness). We predicted 19,502 protein coding genes, with annotation completeness reaching 95.2% BUSCO. Comparative analyses of three Zygaenidae genomes revealed strong conservation of chromosomal synteny and showed that E. westwoodi shares a more similar detoxification gene repertoire with Achelura yunnanensis , another Rosaceae feeder, than with the more divergent, non‐Rosaceae feeding Zygaena filipendulae . Genome‐wide analysis identified 272 detoxification‐related genes, indicating substantial capacity for xenobiotic metabolism. Phylogenetic analysis supported long‐term conservation of a vertically inherited, single‐copy β cyanoalanine synthase (bCAS) gene involved in cyanide detoxification. In addition, structural and phylogenetic analyses revealed parallel retention of CYP405A and CYP332A in the two Rosaceae feeding species, a pattern most parsimoniously explained by the inheritance of an ancestral cyanogenic toolkit rather than by independent convergent recruitment, whereas UGT33A retained the canonical GT‐B fold characteristic of UDP glycosyltransferases, indicating the evolutionary stability of phase II conjugation enzymes. Together, these findings indicate that adaptation in E. westwoodi proceeds through targeted gene‐level evolution within an otherwise conserved genomic framework.