Discovery of an isoflavone biosynthetic pathway in Iridaceae plants

Isoflavones, characterized by their distinctive C6-C3-C6 skeleton, represent an important class of plant secondary metabolites with considerable pharmacological and physiological relevance. Although their biosynthetic pathways have been extensively elucidated in Fabaceae species, the molecular mechanisms governing isoflavone production in other plant families remain largely unexplored. Herein, we uncovered an isoflavone biosynthetic pathway in Iridaceae plants. Notably, it involves an uncharacterized CYP736D family isoflavone synthase, a non-CYP450 (iso)flavone 6-hydroxylase, two cation-dependent type I O-methyltransferases, and a newly identified CYP75F isoflavone 3'-hydroxylase. Evolutionary analyses revealed that Iridaceae have retained an ancient and conserved isoflavone biosynthetic pathway, potentially representing a prototypical route in land plants. In contrast, soybean utilizes a specialized pathway unique to Fabaceae. Our findings not only resolve a long-standing gap in our understanding of isoflavone biosynthesis in Iridaceae plants, but also provide insights into the independent evolutionary trajectory of isoflavone biosynthetic mechanisms in Iridaceae and Fabaceae.