Figure 1.

Engineering Phaeodactylum tricornutum by introducing a plant sapogenin pathway. Schematic representation of sterol metabolism in diatoms starting from the precursor isopentenyl pyrophosphate (IPP) and leading to brassicasterol. In the plant sapogenin pathway, the 2,3‐oxidosqualene precursor is cyclized to lupeol, by a lupeol synthase; the lupeol can be further modified to betulinic acid through a cytochrome P450 family enzyme, along with its coenzyme NADPH reductase. The plant sapogenin pathway enzymes introduced in P. tricornutum will, therefore, compete with the native cycloartenol synthase for the common precursor 2,3‐oxidosqualene.