Abstract
Phytoalexins are abundant in edible crucifers and have important biological activities, yet no dedicated gene for their biosynthesis is known. Here, we report two new cytochromes P450 from Brassica rapa (Chinese cabbage) that catalyze unprecedented S-heterocyclizations in cyclobrassinin and spirobrassinin biosynthesis. Our results provide genetic and biochemical insights into the biosynthesis of a prominent pair of dietary metabolites and have implications for pathway discovery across >20 recently sequenced crucifers.