Biosynthesis of sterol and plant defence compounds share conserved elements

24 March 2014

​Jacob Pollier and Alain Goossens, VIB Department of Plant Systems Biology, UGent, have discovered a new mechanism by which the plant hormone jasmonic acid regulates the production of triterpenoid saponins—plant defense molecules whose biosynthesis pathway shows similarities to sterol synthesis in mammals.

What was the starting point for this research?

Jacob: For a number of years now, our research focus has been on the biosynthesis of plant defense molecules. Specifically, we are looking for positive regulators that, in the long term,
could be used to stimulate the production of certain molecules.

We are mainly using Medicago truncatula, a plant from the legume family that produces a huge
arsenal of bioactive molecules. This study started with a search for activators of triterpenoid saponin synthesis. One of the transgenic Medicago root cultures (with modified expression of a candidate regulator) showed, besides a modified metabolite profile, an extreme morphological phenotype that attracted our attention. After several detours, we were able to determine that this regulator impeded rather than stimulated saponin biosythesis, probably to prevent excessive saponin levels that would be toxic for the plant.

Apparently your research may also offer new insights into sterol synthesis in mammals?

The saponin biosynthesis pathway shares a building block with that of sterols. The regulatory system we discovered in Medicago is based on the same principles as that of sterol synthesis in mammals.

Much is already known about sterol synthesis but a number of basic questions remain as yet
unanswered. We hope that our current work with Medicago will provide new, more detailed insights into the molecular mechanism of this system. Although we focus on plant saponins, we may be able to contribute to an improved understanding of sterol synthesis in other eukaryotes.

The paper in Nature involved collaboration with VIB’s Bio-imaging core. To what extent did this create added value?

In the first place, it gave us major and more accurate insight into the phenotype of the transgenic roots, but it also allowed the Bio-imaging core to optimize its new imaging technologies for use with plant materials. The collaboration is ongoing, by the way, with new Medicago samples and different imaging technologies. We are doing a follow-up study into the regulation of sterol and saponin synthesis and its role in the functioning of plant cells.

Pollier et al., Nature 2013

From left to right: Jacob Pollier, Robin Vanden Bossche, Alain Goossens, Kris Morreel, Anna Kremer, Saskia Lippens, Chris Guérin

©VIB, 2014