Generation of a chromosome-scale genome assembly of the insect-repellant terpenoid-producing Lamiaceae species, Callicarpa americana

Background: Plants exhibit wide chemical diversity due to production of specialized metabolites which function as pollinator attractants, defensive compounds, and signaling molecules. Lamiaceae (mints) are known for their chemodiversity and have been cultivated for use as culinary herbs and as sources of insect repellents, health-promoting compounds, and fragrance.  Findings: We report the chromosome-scale genome assembly of Callicarpa americana L. (American beautyberry), a species within the early diverging Callicarpoideae clade of the Lamiaceae, known for its metallic purple fruits and use as an insect repellent due to its production of terpenoids. Using long reads and Hi-C scaffolding, we generated a 506.1 Mb assembly spanning 17 pseudomolecules with an N50 contig and N50 scaffold size of 7.5 Mb and 29.0 Mb, respectively. A total of 32,164 genes was annotated including 53 candidate terpene synthases and 47 putative clusters of specialized metabolite biosynthetic pathways. Whole genome duplication analyses revealed three putative events, which together with local tandem duplication events, contributed to gene family expa, American beautyberransion of terpene synthases. Kolavenyl diphosphate is a gateway to many of C. americana's bioactive terpenoids; experimental validation confirmed that CamTPS2 encodes kolavenyl diphosphate synthase. Syntenic analyses with Tectona grandis L. f. (teak), a member of the Tectonoideae clade of Lamiaceae known for exceptionally strong wood resistant to insects, revealed 963 collinear blocks and 21,297 C. americana syntelogs. Conclusions: Access to the C. americana genome provides a roadmap for rapid discovery of genes encoding plant-derived agrichemicals and a key resource to understand the evolution of chemical diversity in Lamiaceae.