Unlocking nutritional potential: The bronze tomato's enhanced antioxidant and health properties through metabolic engineering

The Bronze tomato, a product of metabolic engineering, produces high levels of polyphenol due to over-expression of genes such as VvStSy, AmDel/Rosea1 and AtMYB12. This modification, part of broader efforts to enhance plant nutritional value through specific biochemical alterations, results in ripe fruits with significantly higher antioxidant and anti-inflammatory properties. However, while these tomatoes show increased flavonols, anthocyanins, and stilbenes, the overall impact on other physiological processes and the total nutritional profile requires further exploration.

In April 2022, Horticulture Research published a research entitled by “Engineering the polyphenolic biosynthetic pathway stimulates metabolic and molecular changes during fruit ripening in “Bronze” tomato”. In this study, researchers analyzed the transcriptional and metabolic profiles of the Bronze tomato line at various ripening stages to understand how regulatory and structural transgenes affect primary and secondary metabolisms. 

Researchers initially measured the total content of polyphenols, antioxidant capacity, and soluble solutes from fruit harvested at four different ripening stages. Bronze fruit showed significantly higher polyphenol content and antioxidant capacity compared to the control, with a distinct increase from the breaker stage onward. But soluble solutes, defined by the Brix degrees were slightly reduced in the mature green and breaker stages of the Bronze tomatoes compared to the WT. Then, they measured the level of the monosaccharides glucose and fructose and two organic acids, malic and citric, deriving from the tricarboxylic cycle. The levels of glucose and fructose in Bronze fruit were always lower compared to WT. Malic acid significantly lower at the MG and R stages when compared to WT. Conversely, the level of citric acid was significantly higher in the Bronze tomato. The expression profiles of genes related to energy metabolism were further determined. SUS1 (Sucrose synthase 1) and G6PDH (glucose-6-phosphate dehydrogenase) were repressed at the MG stage, DAHPS (3-deoxy-d-arabino-heptulosonate 7-phosphate synthase) was highly repressed while SK (shikimate synthase) was up-regulated in Bronze fruit compared to WT fruit at the same ripening stages.

The study also explored the Bronze tomato's polyphenol content, revealing significant increases in specific flavonoids and the presence of stilbenes and anthocyanins only in the Bronze line. Most structural genes encoding the enzymes driving the biosynthetic flux towards flavonoids and anthocyanins were significantly up-regulated, particularly from the breaker stage. Additionally, the investigation into the expression of genes involved in anthocyanin transport and sequestration showed significant increases, suggesting enhanced vacuolar transport and cytoplasmic pH homeostasis. Carotenoid content analysis revealed a distinct shift in the lycopene/β-carotene ratio in the Bronze tomato, with a significant increase in β-carotene at later ripening stages. This change was linked to the down-regulation of key carotenoid biosynthetic genes, suggesting a complex interplay between carotenoid and polyphenol pathways and their impact on fruit ripening and nutritional quality.

Overall, these findings underscore the Bronze tomato's potential as a model to investigate the combined effects of polyphenols and β-carotene in preventing inflammation-based human diseases and highlight the broader implications of metabolic engineering in enhancing nutritional quality.

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References

Authors

Aurelia Scarano¹, Carmela Gerardi¹, Eduardo Sommella², Pietro Campiglia², Marcello Chieppa³, Eugenio Butelli^4,* and Angelo Santino^1,*

Affiliations

¹ISPA-CNR, Institute of Science of Food Production, C.N.R. Unit of Lecce, 73100 Lecce, Italy

²Department of Pharmacy, School of Pharmacy, University of Salerno, 84084 Fisciano (SA), Italy

³Department of Public Health, Experimental and Forensic Medicine, Dietetics and Clinical Nutrition Laboratory, University of Pavia, Pavia, Italy

⁴John Innes Centre, Colney Research Park, NRA4 7UH Norwich, UK

About Eugenio Butelli & Angelo Santino

Eugenio Butelli: He is a postdoctoral scientist. Eugenio’s scientific interests range from the regulation of gene expression to the link between food and human health, making use of genetic engineering in tomato as a research tool to address these issues. Eugenio’s research also focuses on citrus, where he is working on the molecular mechanisms involved in the regulation of colour and fruit acidity.

Angelo Santino: His scientific activity is currently focused on the following main research topics: Green biotechnology to improve resistance to abiotic stresses and the nutritional value of plants; Plant lipids and hormones signalling; Purification of recombinant proteins induced in heterologous systems.