Dirigent proteins impart stereoselectivity on the phenoxy radical-coupling reaction, yielding optically active lignans from two molecules of coniferyl alcohol in the biosynthesis of lignans, flavonolignans, and alkaloids and thus plays a central role in plant secondary metabolism (By similarity). Required for seed accumulation of neolignans. Homodimer. Seed coat specific expression. Lacks seed-specific neolignans such as 3-{4-[2-hydroxy-2-(4-hexosyloxy- 3-methoxyphenyl)-1-hydroxymethylethoxy]-3,5-di-methoxyphenyl}acryloylcholine. Belongs to the plant dirigent protein family.