Betalains are a class of plant pigments that are responsible for the characteristic red-violet (betacyanin) or yellow (betaxanthin) color of certain fruits and vegetables.
These naturally occurring, water-soluble and nitrogen-containing pigments are commonly used as food coloring agents. Recently, research findings have brought to the forefront the strong antioxidant potential of betalains, making them potential candidates to produce health foods and combat various diseases. At present, betalains are only produced in plants of the order Caryophyllales and higher fungi. Hence, metabolic engineering has been explored to genetically modify cultivable non-Caryophyllales plants, to enhance the production and scalability of these pigments.
Although transgenic betalain-accumulating plants have been developed over the years, their applications in producing healthcare food resources are yet to be explored.
To address this gap, a collaborative research team from Tokyo University of Science (TUS) and Iwate Biotechnology Research Center, Japan, led by Professor Gen-ichiro Arimura from TUS, attempted to genetically modify potato and tomato plants to produce betacyanin. Their aim was to test the therapeutic efficacy of betacyanin producing tomatoes and potatoes against murine models of colitis and inflammation-inducing macrophages. Their findings were published in Biotechnology & Bioengineering on January 26, 2023.
“We successfully engineered potato tubers and tomato fruits to co-express betacyanin biosynthesis genes [genes for CYP76AD1 from Beta vulgaris, DOD (DOPA 4,5-dioxygenase) and 5GT (cyclo-DOPA 5-O-glucosyltransferase) from Mirabilis jalapa] under the control of suitable promoters," Arimura said. "This enhanced the endogenous accumulation of betanin and isobetanin — two common types of betacyanin — in these transgenic vegetables. The accumulation of these pigments made them appear dark red in color upon maturation, as compared to their wild-type counterparts.”
Since macrophages play an important role in several inflammatory diseases, the team further tested the therapeutic efficacy of these transgenic vegetables in macrophage-like cells (RAW264.7), following immune response stimulation by lipopolysaccharides (LPS). They observed that the extracts of the transgenic tomato fruit exerted higher anti-inflammatory activity compared to their wild-type counterparts. This was attributed to a decrease in the LPS-stimulated transcription of the proinflammatory cytokine gene — a Tnf-α gene, within transgenic cells.
“These findings were in line with the anti-inflammatory effects of transgenic tomato that we observed in the intestines of murine models with dextran sulfate sodium (DSS)-induced colitis. A marked improvement in their body weight loss and disease activity index was observed through the suppression of the DSS-stimulated transcription of proinflammatory genes – genes for Tnf-α, Il6 and Cox-2,” added Arimura, discussing the results derived from the other experiment in mice.
Moreover, the additive and synergistic action of betacyanin with natural fruit components (such as lycopene in tomato) further boosted the amelioration of colitis in murine models. Interestingly, while significant anti-inflammatory effects were observed with transgenic tomato extracts at 100–1000-fold dilutions, this was not the case with transgenic potatoes, despite substantial production of betanin and isobetanin. The reason for this is speculated to be the presence of unknown antagonists in transgenic potatoes that work against betacyanin’s anti-inflammatory function, but is yet to be confirmed.
“Tomatoes genetically engineered to produce betacyanins were found to have substantial health promoting effects. Although natural plant sources of betalains such as beetroots exist, these pigments demonstrate poor stability in high temperatures and extreme pH. This indicates that betacyanin producing transgenic tomato lines are more likely to be effective as health foods when ingested in their raw state,” said Arimura. "What are the potential applications of these findings? Although there is no commercial cultivation of edible genetically modified crops in Japan, we expect that their applications as health foods through production in enclosed plant factories and other facilities will lead to the widespread use of recombinant plants in Japan.
"We are confident that betalain engineering will soon become a promising avenue to improve the commercial production of health foods, that boost food supply while simultaneously conferring health benefits to its consumers."