Carotenoid hydroxylation--P450 finally!

Cytochrome P450 monooxygenases are involved in the biosynthesis of various compounds in plants such as phenylpropanoids, lipids and phytohormones. Hydroxylation of the carotenoid epsilon-ring is an essential reaction for the formation of lutein, the most abundant carotenoid in photosynthetic tissues. Recently, Li Tian and colleagues reported that a new P450 is responsible for this reaction. This discovery not only adds to the list of various functions of plant cytochrome P450s but also identifies one of the missing pieces of the puzzle of carotenoid biosynthesis.