Metabolic Engineering of Isoflavone Biosynthesis in Seeds

This chapter reviews studies on the physiological effects of isoflavones, highlighting both the benefits and risks of isoflavone consumption to different populations of people. It focuses on metabolically engineering isoflavones. The chapter outlines the biosynthetic pathway and also focuses on a few key biosynthetic enzymes and the traditional genetic approaches to identify major determinants of soybean isoflavone levels. It summarizes engineering feats that have resulted in different isoflavone levels in soybean, model plants, and nonlegume crops. To understand the accumulation of isoflavones in soybean, it is necessary to understand the functions of isoflavones in plants, i.e., to understand why and under what conditions isoflavones are synthesized. Isoflavones are the major inducers of nod gene expression in their most common symbiont, Bradyrhizobium japonicum. Isoflavones are specifically recognized by nodD receptor on cell surfaces of B. japonicum. Flavanones are the branching point of flavonoid and isoflavonoid biosynthesis.