Improving grain protein quality by genetic engineering: some biochemical considerations

Abstract

Cereals are usually deficient in lysine, legumes in methionine and cysteine. The use of genetic engineering to improve grain/seed protein quality include: enhancing selectively the expression of, and increasing the gene copy number of, nutritionally rich storage protein genes, modifying existing storage protein genes to code for more of the essential amino acids, and transferring genes for nutritionally rich, storage proteins from heterologous species into desired crops. As methionine and lysine are both derived from aspartate, manipulation of genes encoding enzymes involved in amino acid interconversions can be used to improve the amino acid balance, or to alter the amounts of amino acids reaching the grain through phloem translocate, which itself is low in lysine and methionine.