People often turn to a plant-rich diet when they want to reduce their cholesterol intake. But plants often make the complicated sterol too, albeit at a level that’s at least two orders of magnitude less than that made by animals: Cholesterol can be found in leaf lipids, can be used to make a precursor for vitamin D-3, and can be turned into herbivore-deterrents and pathogen poisons, such as α-solanine in potatoes and α-tomatine in tomatoes.
Now, more than two centuries after French chemists first discovered cholesterol in human gallstones, scientists have figured out how plants make the useful molecule. A team of scientists led by Asaph Aharoni at the Weizmann Institute of Science identified the 12 enzymes and 10 chemical conversions used by the tomato plant to convert 2,3-oxidosqualene to cholesterol (Nat. Plants 2016, DOI: 10.1038/nplants.2016.205). They found that the biosynthetic pathway for cholesterol overlaps with the metabolic pathway for phytosterols, the more common and abundant variety of sterols in plants. For example, both pathways share four enzymes, and both use the same precursor. Aharoni’s team proposes that the cholesterol biosynthetic pathway likely evolved from the phytosterols metabolic route.
The discovery of the cholesterol pathway could find use in synthetic biology applications. The work, for instance, “could be a first step toward plant-based engineering of interesting cholesterol derivatives,” writes Thomas J. Bach at the University of Strasbourg, in a commentary associated with the new study (Nat. Plants 2016, DOI: 10.1038/nplants.2016.213).