Purple tomatoes thanks to a red beet pigment

Some researchers of the Leibniz Institute for Plant Biochemistry (IPB) in Halle, Germany, have recently created purple tomatoes by using genetic engineering methods. To do this, they inserted the genes responsible for betanin biosynthesis in the plant and activated them in the ripening fruit. Betanin is not normally produced by tomatoes, but extracted from red beet and used as natural food coloring. This type of genetic engineering methods help produce substances in specifically developed plant production systems. It will definitely play an important role in the future, especially to produce medication. Manufacturing vaccines and antibodies with plants already is a very active field of research.

Thus, the main objective of this study was not to create a new tomato variety for consumption, but rather to refine the methods of genetic engineering, which are much easier to analyze by producing a clearly visible pigment. Plants are very efficient but also very complicated production systems. They have a large number of regulatory mechanisms that can sometimes slow down the entire biosynthesis process of the substance to produce. “These complex feedback mechanisms are still poorly understood,” explains Sylvestre Marillonnet, lead researcher of the study. “A lot of research is still needed in this regard.”

Even for the betanin, it took a lot of planning and adjustments for the plants to achieve the desired synthesis yield. The Halle researchers inserted the three genes needed for betanin biosynthesis into the tomato plants, and they also inserted several genetic switches to activate the inserted genes only in the fruit and at exactly the same time during ripening. Still, the betanin production in the fruit was meager at first. A fourth gene had to be inserted, ensuring the provision of an important precursor substance, in order to maintain a higher biosynthesis level of the pigments. This is how the deep purple tomatoes were born, containing even more betanin than red beets. 

The Halle study provided new important information on genetic engineering methods. “But these tomatoes are also perfectly safe for consumption and even very healthy.” Indeed, betanin, like many pigments, has a strong antioxidant effect. The purple fruits could also be a source of betanin, a food coloring agent. The first attempts at using betanin from tomatoes to color yoghurts and lemonades gave promising results.

Besides genetic engineering - the production of substances in plants - IPB conducts extensive research on all conventional methods of production of active ingredients from plants. This includes the traditional organic synthesis and the development of biotechnological methods to produce the desired products thanks to bacteria or yeast. The relatively immature and promising method of biocatalysis is also studied at the institute. This method consists of using genetic engineering to modify the genes of the biosynthesis enzymes of the plants in order to create new enzymes with the desired properties. These new enzymes are then used to develop new processes for the synthesis of the desired products in test tubes. The method chosen depends on the structural properties of the substance to be produced. Some plant compounds, like morphine and other opiates, have such a complex structure that it is even more economic to extract them directly from the plant.

For more information:
Dr. Sylvestre Marillonnet
Leibniz-Institut für Pflanzenbiochemie

Photo: © Sylvestre Marillonnet, IPB

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