ABSTRACT
Animals, including humans, are incapable of synthesizing 10 of the 20 amino acids required for protein synthesis. Consequently, these essential amino acids must be obtained from the diet. A de - ciency in essential amino acids leads to malnutrition, resulting in growth retardation and/or even death. However, most crop plants have a poor balance of the amino acids essential for the needs of humans and animals. Among the essential amino acids, lysine (Lys), tryptophan (Trp), methionine (Met), and cysteine (Cys) have received the most attention because they are the most limiting in cereal (Lys and Trp) and legume crops (Met and Cys). To enrich crop plants with the desired amino acids, three approaches have been used: (1) the selection of mutants with an increased desired
11.1 Improving the Amino Acid Balance in Crop Plants by Genetic Engineering ..................... 157 11.1.1 Improving Lys Content by Genetic Engineering ...................................................... 158 11.1.2 Improving Met Content by Genetic Engineering ..................................................... 159 11.1.3 Improving Trp Content by Genetic Engineering ...................................................... 161
11.2 Improving the Fatty Acid Composition in Oilseed Crops by Genetic Engineering ............. 162 11.2.1 Improving the Medium-Chain Fatty Acid Content by Genetic Engineering ........... 162 11.2.2 Improving Saturated Fatty Acid Content by Genetic Engineering .......................... 163 11.2.3 Improving Oleic Acid Content by Genetic Engineering .......................................... 164 11.2.4 Improving Long-Chain Polyunsaturated Fatty Acid Content
by Genetic Engineering ............................................................................................ 164 11.3 Improving the Bioavailability of Minerals and Vitamins by Genetic Engineering ............. 165
11.3.1 Improving Vitamin Contents in Crop Plants by Genetic Engineering ..................... 165 11.3.2 Improving the Mineral Bioavailability of Crop plants by Genetic Engineering ...... 166
11.4 Eliminating Allergens by Genetic Engineering ................................................................... 168 11.5 Eliminating Toxins by Genetic Engineering ........................................................................ 168 11.6 Production of an Edible Vaccine by Genetic Engineering ................................................... 169 11.7 Future Perspectives ............................................................................................................... 171 References ...................................................................................................................................... 172
amino acid content, (2) genetic modi cation to promote the biosynthesis of the desired amino acids, and (3) genetic modi cation to increase the contents of the desired amino acids in storage proteins. Unfortunately, conventional genetic approaches have met with limited success due mostly to the limited availability of genetic resources for breeding. In addition, genetic traits for a high content of Lys, Trp, or Met are generally associated with abnormal growth and development. Recent advances in genetic engineering appear to offer much promise because they allow the seed-speci c expression of speci c traits of interest using seed-speci c promoters. Another advantage of genetically engineered traits is that they can be transformed into multiple plant species and genotypes and can function synergistically with many other agronomically important traits. The current status of and potential developments in the improvement of Lys, Met, and Trp content in crop plants using a transgenic approach are presented here.
