Making Plant Hormones in the Lab

Plants produce the hormone jasmonic acid as
a defense response when challenged. This is how they ensure that their
predators no longer like the taste of their leaves. Biologists want to find out
whether biological precursors and other variants of jasmonic acid lead to
similar or different effects. But such derivatives of the hormone have so far
been too expensive for experiments and difficult to come by. Researchers from
the Faculties of Chemistry and Biology at Bielefeld University have now found a
method that might make the production of a biologically significant precursor
of jasmonic acid more efficient and cheaper. Their innovation: they imitate how
plants produce the hormone. The result is 12-OPDA, a central precursor of
jasmonic acid. In the long term, it could also be a potential precursor for
high-quality perfume. The researchers present their method in the research
journal Advanced Science.

“Jasmonic acid can, for example, trigger
the release of toxic substances such as nicotine in the leaves, which harms
predators,” explains biologist Professor Dr Karl-Josef Dietz. “Tobacco plants
emit a modified form of jasmonic acid which induces neighbouring plants to
prepare for attacks,” says Dietz. “Jasmonic acid also supports healing and can
stimulate damaged plants to regenerate.”

Dietz heads the Plant Biochemistry and
Physiology Working Group at Bielefeld University. He is researching how plants
react to stress and is working on changing and optimizing their response. “This
will enable us to prepare plants for the new environmental conditions resulting
from climate change, for instance.” If the warmer climate leads to an increase
in beetle populations, plants could be equipped with the ability to harm these
attackers with bitter substances. “We are interested in the effect of preforms
of jasmonic acid, such as 12-OPDA, which is only available in the milligram
range and then costs several hundred euros,” says Dietz.

“The high price is due to the
labour-intensive production process, as the production of 12-OPDA is extremely
complex and involves numerous reaction steps in the classical chemical process,”
says chemist Professor Dr Harald Gröger. He heads the Industrial Organic
Chemistry and Biotechnology Working Group at Bielefeld University. Together
with Dietz, he developed the idea of producing 12-OPDA (12-oxophytodienoic
acid) as a precursor of jasmonic acid by means of an efficient and innovative
synthetic method. Both scientists conduct research at the Center for
Biotechnology (CeBiTec) at Bielefeld University.

The new method adopts the principle from
plant cells: it uses enzymes as plant catalysts in a form optimized for
synthetic purposes. “It is important that these enzymes are used in the right
ratio,” says Jana Löwe. She is the lead author of the new study and a
researcher in Gröger's working group. The best part of the new method is that
if all the initial conditions are correct, it subsequently runs on its own.

“Like plants, we use easily accessible
linolenic acid in combination with only three enzyme reactions,” explains Löwe.
Linolenic acid can be extracted from rapeseed oil, for example. The first
enzyme incorporates oxygen from the air into the linolenic acid. The second
enzyme subsequently produces a highly unstable intermediate, which is then
converted into 12-OPDA by the third enzyme.

“It sounds simple,” says Gröger. “The
difficulty so far, however, has been the sensitive, short-lived intermediate
stage created by the second enzyme. If the third enzyme is not added
immediately, the resulting products are unusable.”

Löwe solves the problem by using bacteria
as producers of the enzymes for the second and final stage of the reaction – in
combination with a commercial enzyme derived from soybeans for the first
reaction stage. The bacteria (Escherichia coli) have been genetically
modified to provide the two enzymes in the required quantities. “As soon as the
unstable intermediate is formed, the required enzyme is immediately available
and ensures the production of 12-OPDA,” says Löwe.

The 12-OPDA can then be used directly in
biological studies or converted into other substances needed for Dietz's
experiments, for example. Löwe has also developed a method for this. “This
provides us with a library of descendants of 12-OPDA for plant physiological
investigations,” says Dietz. “With further reactions, the 12-OPDA could even be
used to produce methyl dihydrojasmonate efficiently in the future,” says
Gröger. “This is a substance required as an ingredient in many well-known
perfumes.”

Reference

Löwe et al. (2020). From a
biosynthetic pathway toward a biocatalytic process and chemocatalytic
modifications: Three-step enzymatic cascade to the plant metabolite
cis-(+)-12-OPDA and metathesis-derived products. Advanced Science. DOI: https://doi.org/10.1002/advs.201902973

This article has been republished from the
following materials.
Note: material may have been edited for length and content. For further
information, please contact the cited source.