Abstract
Humans and animals are unable to synthesize essential amino acids such as branch chain amino acids methionine (Met), lysine (Lys) and tryptophan (Trp). Therefore, these amino acids need to be supplied through the diets. Several essential amino acids are deficient or completely lacking among crops used for human food and animal feed. For example, soybean is deficient in Met; Lys and Trp are lacking in maize. In this mini review, we will first summarize the roles of essential amino acids in animal nutrition. Next, we will address the question: "What are the amino acids deficient in various plants and their biosynthesis pathways?" And: "What approaches are being used to improve the availability of essential amino acids in plants?" The potential targets for metabolic engineering will also be discussed, including what has already been done and what remains to be tested.