Nature Biotechnology pp 177 - 181

Scientists in Spain have identified a gene from strawberry responsible for the synthesis of vitamin C (ascorbic acid), opening the path to new types of foods and plants with boosted levels of the vitamin. In the February issue of Nature Biotechnology, Victoriano Valpuesta and colleagues describe the isolation of the GalUR gene, encoding an enzyme that plays a role in the conversion of D-galacturonic acid to ascorbic acid in strawberry fruit. Overexpression of the enzyme's gene in the small weed thale cress (Arabidopsis thaliana) enhances vitamin C content two- to threefold, demonstrating the feasibility of engineering increased vitamin C levels in plants using this enzyme.

Ascorbic acid is crucial to the maintenance of a healthy immune system and plays a vital role in the human body as an antioxidant. The synthesis of vitamin C in plants has remained poorly understood until the recent identification of a pathway in which ascorbic acid is synthesized from L-galactose. An additional pathway had also been suggested, and now Valupesta and coworkers provide evidence for this alternative synthetic route. Identification of genes involved in ascorbic acid synthesis and accumulation could provide tools for increasing vitamin C content of food crops. Manipulation of these genes could also contribute to the understanding of ascorbic acid's function in plant stress resistance. What's more, microbes and bugs might be engineered with the enzyme allowing ascorbic acid biosynthesis and providing an alternative basis for the manufacture of vitamin C.

Nature Biotechnology pp 157 - 162

Milk enhanced in protein promises to transform the speed and ease of cheese-making. Researchers in New Zealand have succeeded for the first time in generating cloned cows that produce milk with potentially improved processing properties and heat stability. In the February issue of Nature Biotechnology, scientists at AgResearch in Hamilton, New Zealand, engineered cow cells in the laboratory to overproduce milk proteins called casein. Nuclear fusion of these transgenic cells with cow eggs, and transfer of the corresponding embryos into recipient cows, resulted in the birth of eleven transgenic calves, nine of which produce highly elevated levels of casein in their milk.

The transgenic calves produced by Götz Laible and colleagues carry extra copies of two casein genes, beta-casein and kappa-casein. On reaching maturity, nine of these cows produced milk with 8 to 20% more beta-casein and a twofold increase in kappa-casein. Controlled changes in these major components of milk could result in improved processing characteristics, such as improved cheese-making properties, reduced rennet clotting time and increased whey expulsion. The generation of transgenic livestock with altered milk composition thus holds great potential for applications in the food industry. While cows had been previously engineered to produce proteins of pharmaceutical interest, this is the first instance in which the properties of cow milk itself have been altered to achieve milk with improved characteristics.