Fig. 2.

Proposed pathways of fucoxanthin biosynthesis in algae. The fucoxanthin biosynthetic pathway and pathway-specific enzymes in algae with diadinoxanthin cycle such as diatoms and haptophytes are labeled in brown, those in algae with violaxanthin cycle such as brown algae are labeled in khaki; question marks denote the steps catalyzed by unknown enzymes. Intermediates labeled in green accumulate in the respective KO mutants of the diatom P. tricornutum (see Fig. 1C). Note that the acetylation steps (Ac) in both pathways are predicted to occur on opposite rings (A or B) of their last common precursor neoxanthin. Dashed red arrows denote high light-induced xanthophyll cycle activity, dotted blue arrows denote back reactions catalyzed in low light. VDE, violaxanthin de-epoxidase; VDL, violaxanthin de-epoxidase-like; ZEP, zeaxanthin epoxidase.