Lysine, Methionine, Threonine and Tryptophan are considered as most important amino acids for human health. However, the nutritive and biological value of the protein can be increased by balanced composition of essential amino acids. Methionine is the primary limiting essential amino acid in grain legumes. Little or no effort has been made for improvement of the biological value of grain legumes by conventional breeding. Therefore, genetic engineering may prove as a potential approach to nutritive quality of grain legumes. The biotechnological strategies for improving nutritional quality considered important are i) Engineering for free methionine levels, ii) Engineering of endogenous storage proteins, iii). Efficient transformation system. The later strategy turned out to be most promising although legumes are still difficult to transform. Nutritional deficiencies of legumes, the biochemical, physiological or molecular basis is not completely understood. Moreover, modifications meant to improve nutritional quality may create undesired side-effects. Transgenic approaches will undoubtedly be instrumental to resolve these issues. Gene transfer experiments with soybean. lupin and narbon bean have revealed that the introduction of genes encoding foreign proteins will successfully improve grain legumes with high seed Met levels. Thus, within a measurable space of time we can expect that due to the employment of genetic engineering grain legumes varieties will be bred and brought to market which are improved in amino acid composition of their total seed protein. The present review summarizes the possible methods for improving nutritive quality of grain legumes through genetic engineering.
Essential amino acids, metabolic engineering, nutritional quality, biotechnology
