Polyploidy underlies co-option and diversification of biosynthetic triterpene pathways in the apple tribe

Significance Plants are a primary source of both traditional and modern drugs due to their astounding capability to synthesize diverse molecules. The fruit tree loquat in the apple tribe has been long used in medicine to treat cough, chronic bronchitis, and asthma, yet why loquat—but not its relatives—evolved these medicinal properties is unknown. Here, we generate high-quality genomes of loquat and a relative, which are separated by a recent whole-genome duplication (WGD) around 13.5 to 27.1 Mya. We revealed the post-WGD diversification of triterpene biosynthesis and the exceptionally high levels of bioactive ursane-type triterpenes specifically in loquat. Our work underscores the importance of WGD-associated metabolic diversification underlying the bioactivity of some medicinal plants.