Selectively enriching valuable ingredients of chicory.
Cichorium intybus is a widespread plant whose cultivated forms are also known as chicory or radicchio. Root chicory (Cichorium intybus var. sativum), used as a coffee substitute in the past, is nowadays grown mainly for the production of inulin. Inulin is a fructose polymer and serves as a prebiotic dietary fiber and low-calorie sweetener in food processing. Furthermore, chicory taproots contain sesquiterpene lactones (STLs). This group of secondary plant metabolites consists of about 5000 different compounds that have a typical C15 terpene structure with a lactone ring, as well as anti-inflammatory, anti-cancer, or analgetic bioactivity. In chicory, bitter compounds such as lactucin, 8-deoxylactucin, lactucopicrin, and their oxalates are among the STLs that are the major bitter components of the plant's latex.
The first steps in the biosynthesis of these STLs were already known up to the intermediate costunolide. Now, scientists at Wageningen University and IPB have succeeded in elucidating the biosynthesis step downstream of costunolide. Since this intermediate has anti-cancer bioactivity and may be useful for developing therapeutics but is almost completely converted to STLs in the biosynthetic pathway, the research team also aimed to block the downstream biosynthetic steps so that costunolide accumulates. This would achieve two useful goals at once: reducing bitter substances in the chicory root and opening a way to obtain the valuable, bioactive costunolide.
Using sequence similarities to related enzymes from feverfew, the research team identified three cytochrome P450 enzymes in chicory that convert costunolide to the next intermediate, kauniolide. Using genome editing with CRISPR/Cas9, they were able to knock down these kauniolide synthases and generate plant lines that no longer produced STLs but instead accumulated greater amounts of costunolide but also costunolide conjugates, as expected. In doing so, they present a strategy for making better use of chicory's valuable terpenes in the future.
The study was conducted as part of the EU Horizon2020-funded consortium project on the Application of New Plant Breeding Techniques for producing high-value products in the multipurpose crop chicory.
Original publication:
Cankar K, Hakkert JC, Sevenier R,Campo E, Schipper B, Papastolopoulou C, Vahabi K, Tissier A, Bundock P and Bosch D (2022) CRISPR/Cas9 targeted inactivation of the kauniolide synthase in chicory results in accumulation of costunolide and its conjugates in taproots. Front. Plant Sci. 13:940003. doi: 10.3389/fpls.2022.940003
