Bioprocess developed for plant hormone
The plant hormone jasmonic acid is widely used, but the chemical synthesis of the precursor 12-OPDA is expensive. Researchers have now biotechnologically imitated the production process.
Scientists at Bielefeld University have succeeded for the first time in enzymatically producing 12-oxophytodienoic acid (12-OPDA), a central precursor of the plant hormone jasmonic acid. The jasmonates are derived from the acidity, by means of which plants react to injuries, warn each other of pests or also control fruit ripening: "For example, jasmonic acid can trigger the release of toxic substances such as nicotine in the leaves, which harm the attackers", explains biologist Karl-Josef Dietz. "Jasmonic acid also has healing properties and can induce damaged leaves to regenerate."
Chemical synthesis is complex
Plant researchers are very interested in jasmonic acid and its precursors in order to produce improved varieties through breeding. For example, if certain feeding insects become more frequent as a result of climate change, plants would be better able to defend themselves against them by increasing their production of jasmonic acid. But just a few milligrams of 12-OPDA already cost several hundred euros. "The high price is due to the labour-intensive production process, since the production of 12-OPDA is extremely complex and involves many reaction stages using classical chemical methods", explains chemist Harald Gröger, who is also involved in the research project.
Enzyme steps of the plant reproduced
Together, the Bielefeld researchers have now reconstructed the plant's path to the formation of the hormone in order to produce 12-OPDA biotechnologically: "Like the plants, we use the easily accessible linolenic acid in combination with only three enzyme reactions" explains Jana Löwe, first author of the study published in the journal "Advanced Science". While linolenic acid can be easily extracted from rapeseed oil, the three reaction steps of the enzymes must be precisely coordinated. "The difficulty so far has been the sensitive, short-lived intermediate stage that is created by the second enzyme," explains Gröger. "If the third enzyme isn't added here immediately, it creates useless products."
The solution to the problem was to optimise the bacterium Escherichia coli so that it produced the enzymes for steps two and three in the right quantities. "As soon as the labile intermediate is formed, the required enzyme is immediately available and ensures the production of 12-OPDA" Löwe explains the trick. The first step is a simple one using a commercially available enzyme from soybeans.
Inexpensive material for further research
The resulting 12-OPDA can now be used directly for research or converted into other products that are relevant for plants. "This provides us with a library of descendants of 12-OPDA for plant physiological studies", Dietz is pleased. And the scientists see yet another purpose for the new and inexpensive process: "Through further reactions, the 12-OPDA might even be able to efficiently produce methyl dihydrojasmonate in the future," hopes Gröger. "This is a substance required as an ingredient in many popular perfumes."
The project was funded through the initiative "Nächste Generation biotechnologischer Verfahren – Biotechnologie 2020+" of the Federal Ministry of Education and Research.