Metabolic Engineering of Isoflavone Biosynthesis

Isoflavones are phenolic secondary metabolites found mostly in legumes. These compounds play key roles in many plant–microbe interactions and are associated with the health benefits of soy consumption. Because of their biological activities, metabolic engineering of isoflavonoid biosynthesis in legume and nonlegume crops have significant agronomic and nutritional impact by enhancing plant disease resistance and providing dietary isoflavones for the improvement of human health. This review first outlines the current understanding of isoflavone biosynthetic pathways, with focus on key structural enzymes and transcription factors that directly relate to the pathways. Then it summarizes recent progress on metabolic engineering of isoflavone biosynthesis in both legume and nonlegume plants. The major limitations of these approaches, as well as the “metabolic channeling” theory, which is proposed to explain some of the results from the engineering works, are also discussed.