Identification of an isoflavone 6-hydroxylase involved in tectorigenin biosynthesis in kudzu (Pueraria montana var. lobata) and the efficient production of 6-methoxyisoflavones

Abstract

Kudzu (Pueraria montana var. lobata) produces several isoflavones that have beneficial effects in humans. These isoflavones accumulate in a tissue-specific manner, with 5, 7, 4′-trihydroxy-6-methoxyisoflavone (tectorigenin) and its derivatives accumulating mainly in flowers. Tectorigenin has various beneficial effects on humans and is in high demand, but its biosynthesis has not been elucidated, making large-scale production difficult. In this study, we elucidated the steps in tectorigenin biosynthesis in kudzu by identifying a novel isoflavone 6-hydroxylase and isoflavone O-methyltransferase through a transcriptome analysis and related enzyme assays. Furthermore, using yeast engineered to express genes encoding these enzymes, we successfully produced the 6-methoxyisoflavones tectorigenin, glycitein, and afrormosin from the inexpensive isoflavones genistein, daidzein, and formononetin, respectively. The tectorigenin production rate was 40 mg l⁻¹ after being cultured for 72 h. These results contribute to large-scale tectorigenin production and to tectorigenin-related research.