Unusual P450 reactions in plant secondary metabolism

Plant cytochromes P450 (P450s) participate in a variety of biochemical pathways to produce a vast diversity of plant natural products. The number of P450 genes in plant genomes is estimated to be up to 1% of the total gene annotations of each plant species, implying that plants are huge sources for various P450-dependent reactions. Plant P450s catalyze a wide variety of monooxygenation/hydroxylation reactions in secondary metabolism, and some of them are involved in unusual reactions such as methylenedioxy-bridge formation, phenol coupling reactions, oxidative rearrangement of carbon skeletons, and oxidative C–C bond cleavage. Here, we summarize unusual P450 reactions in various plant secondary metabolisms, and describe their proposed reaction mechanisms.

Research highlights
► Unusual P450 reactions in isoquinoline alkaloid biosynthesis and other plant secondary metabolisms are presented.
► The proposed mechanisms of unusual P450 reactions such as phenol coupling, rearrangement of carbon skeletons, C–C bond cleavage, and methylenedioxy-bridge formation are described.
► Implication of the conserved threonine residue for unusual P450 reactions is discussed.