Increased Production of Nutriments by Genetically Engineered Crops

Abstract

Plants are the basis of human nutrition and have been selected and improved to assure this purpose. Nowadays, new technologies such as genetic engineering and genomics approaches allow further improvement of plants. We describe here three examples for which these techniques have been employed. We introduced the first enzyme involved in fructan synthesis, the sucrose sucrose fructosyltransferase (isolated from Jerusalem artichoke), into sugar beet. The transgenic sugar beet showed a dramatic change in the nature of the accumulated sugar, 90% of the sucrose being converted into fructan. The use of transgenic sugar beet for the production and isolation of fructans will result in a more efficient plant production system of fructans and should promote their use in human food. The second example shows how the over-expression of the key enzyme of flavonoid biosynthesis could increase anti-oxidant levels in tomato. Introduction of a highly expressed chalcone isomerase led to a seventyfold increase of the amount of quercetin glucoside, which is a strong anti-oxidant in tomato. We were also able to modify the essential amino acid content of potato in order to increase its nutritional value. The introduction of a feedback insensitive bacterial gene involved in biosynthesis of aspartate family amino acids led to a sixfold increase of the lysine content. Because the use of a bacterial gene could appear to be controversial, we also introduced a mutated form of the plant key enzyme of lysine biosynthesis (dihydrodipicolinate synthase) in potato. This modification led to a 15 times increase of the lysine content of potato. This increase of the essential amino acid lysine influences the nutritional value of potato, which normally has low levels of several essential amino acids. These three examples show how the metabolism of primary constituents of the plant cell such as sugar or amino acids, but also of secondary metabolites such as flavonoids, can be modified by genetic engineering. Producing fructan, a soluble fiber, increasing the level of flavonoids, an antioxidant, in tomato or increasing the level of essential amino acids in potato are all clear examples of plant genetic modifications with possible positive effects on human nutrition.

• genetic engineering
• plant
• fructan
• amino acids
• flavonoids

Key teaching points:

• Research indicates that dietary fructans, such as inulin, and flavonoids may have important health-promoting properties. Current dietary consumption of these nutriments may be suboptimal for realizing their benefits.

• Sugar beets have been genetically engineered to contain enzymes that efficiently convert sucrose to fructans. These sugar beets could provide an additional source of fructans for use as a food ingredient in a greater variety of foods.

• Initial studies have shown it is possible to engineer tomatoes genetically to overexpress the enzyme responsible for synthesis of flavonol in tomatoes.

• A single amino acid residue change in the potato enzyme responsible for lysine synthesis makes it much less susceptible to feedback inhibition such that the concentration of lysine in potato can be greatly increased.

• Modern biotechnology is proving to be a powerful tool to improve the nutritional quality of crop foods when combined with traditional plant breeding and genetic resource management.

Key teaching points:

• Research indicates that dietary fructans, such as inulin, and flavonoids may have important health-promoting properties. Current dietary consumption of these nutriments may be suboptimal for realizing their benefits.

• Sugar beets have been genetically engineered to contain enzymes that efficiently convert sucrose to fructans. These sugar beets could provide an additional source of fructans for use as a food ingredient in a greater variety of foods.

• Initial studies have shown it is possible to engineer tomatoes genetically to overexpress the enzyme responsible for synthesis of flavonol in tomatoes.

• A single amino acid residue change in the potato enzyme responsible for lysine synthesis makes it much less susceptible to feedback inhibition such that the concentration of lysine in potato can be greatly increased.

• Modern biotechnology is proving to be a powerful tool to improve the nutritional quality of crop foods when combined with traditional plant breeding and genetic resource management.