Phylogenetic Links in Plant Defense Systems: Lignans, Isoflavonoids, and Their Reductases

Many lignans and isoflavonoids derived from (+)-pinoresinol/ (+)-lariciresinol and isoflavone reductases, respectively, have important roles in plant defense against pests and pathogens. In addition to their somewhat comparable physiological functions, other similarities are noted between these apparently unrelated branches of phenylpropanoid metabolism which suggest a phylogenetic link. These include similar enzymatic mechanisms, gene sequence homology, and putatively conserved protein phosphorylation sites for the pivotal branch point reductases, as well as comparable roles in [inducible] defense systems. Taken together with a detailed chemotaxonomic analysis of metabolite occurrence, it is proposed that during plant evolution, (+)-pinoresinol/(+)-lariciresinol reductase served as progenitor of the isoflavone reductases.