Researchers from the University of Hong Kong (HKU), together with the
Institut de Biologie Mol¨?culaire des Plantes (CNRS, Strasbourg, France),
have identified a new strategy to simultaneously enhance health-promoting
vitamin E by ~6-fold, as well as double both provitamin A and lycopene
contents in tomatoes, to significantly boost antioxidant properties.

The research group manipulated the plant isoprenoid pathway by using 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 (?Á-tocopherol) by
494%. The HMGS DNA used in the experiment is from Indian mustard (Brassica
juncea), a food crop.

The group reported earlier that the recombinant HMGS variant S359A shows
10-fold higher enzyme activity, and increased phytosterol content in the
model plant Arabidopsis. The researchers introduced the S359A into tomatoes.
There were no differences in the appearance and size of the transformed
tomato fruits, but the total carotenoids including provitamin A and lycopene
increased drastically by 169% and 111%, respectively. The carotenoid
extracts have 89.5-96.5% higher antioxidant activity than the control, and
the transformed tomatoes displayed elevations in vitamin E (?Á-tocopherol,
494%), squalene (210%), and phytosterols (94%).

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