GM tomato gives added value

Hong Kong researchers produce tomatoes with extra vitamins, antioxidants

THE School of Biological Sciences, Faculty of Sci­ence, the University of Hong Kong (HKU), in col­laboration with the Institut de Biologie Moléculaire des Plan­tes (CNRS, Strasbourg, France), has identified a new strategy to simultaneously enhance health-promoting vitamin E by ~6-fold and double both provitamin A and lycopene contents in tomatoes, to significantly boost antioxidant properties.

The research group manip­ulated the plant isoprenoid pathway through the utilisation of a variant of 3-hydroxy-3-meth­ylglutaryl-coenzyme A synthase (HMGS). The overexpression of HMGS in tomatoes increased not only phytosterols, squalene, pro­vitamin A and lycopene, but also vitamin E (α-tocopherol) by 494 percent.

The HMGS DNA used in these experiments originated from a food crop, Brassica juncea (Indian mustard), that yields edible leaves, stems and seeds, the latter used in vegetable oil production. Earlier, this research group reported that the recom­binant HMGS variant S359A (in which amino acid residue “serine” at position 359 was switched to “alanine”) exhibits ten-fold higher enzyme activity. The introduction of S359A in the model plant Ara­bidopsis increased phytosterol content.

Now, the research group has introduced the S359A into toma­toes, a crop plant. Although there were no differences in the appearance and size of the transformed tomato fruits, total carotenoids including provitamin A and lycopene increased dras­tically by 169 percent and 111 percent respectively, as observed by a deeper colour of carotenoid extracts in S359A tomatoes over the control. Furthermore, these carotenoid extracts exhibited 89.5-96.5 percent higher antioxi­dant activity than the control.

Besides carotenoids, the transformed tomatoes dis­played elevations in vitamin E (α-tocopherol, 494 percent), squalene (210 percent), and phytosterols (94 percent). These observations were attributed to the increased expression of genes in the isoprenoid pathway.

Professor Chye Mee-len who led this research said: “Increasing health-promoting components in crops is an important research area that aligns with the aspira­tions of Dr Wilson and Amelia Wong on the use of plant biotech­nology for a sustainable future.

The accumulation of the healthy components in food crops would provide added-value to fruits and vegetables in the human diet, as well as enrich feed for livestock and aquacul­ture.”

Dr Wang Mingfu added: “Extracts with enriched phytos­terols, vitamin E and carotenoids can be used in the production of anti-ageing cream and sun-care lotion. These compounds show excellent anti-inflammatory and antioxidant activity.”