Abstract
The essential amino acids lysine and threonine are synthesized in higher plants via a pathway starting with aspartate that also leads to the formation of methionine and isoleucine. Lysine is one of most limiting amino acids in plants consumed by humans and livestock. Recent genetic, molecular, and biochemical evidence suggests that lysine synthesis and catabolism are regulated by complex mechanisms. Early kinetic studies utilizing mutants and transgenic plants that over-accumulate lysine have indicated that the major step for the regulation of lysine biosynthesis is at the enzyme dihydrodipicolinate synthase. Despite this tight regulation, recent strong evidence indicates that lysine catabolism is also subject to control, particularly in cereal seeds. The challenge of producing crops with a high-lysine concentration in the seeds appeared to be in sight a few years ago. However, apart from the quality protein maize lines currently commercially available, the release of high-lysine crops has not yet occurred. We are left with the question, is the production of high-lysine crops still a challenge?
Highlights
Hunger and malnutrition are among the most devastating problems affecting a large part of the world’s population
Cereals are usually deficient in lysine, threonine and tryptophan, while legumes are deficient in methionine
AK catalyzes the phosphorylation of aspartate to ß-aspartyl phosphate, which is converted to ß-aspartyl semialdehyde (ASA) in a reaction catalyzed by the enzyme aspar
Summary
Hunger and malnutrition are among the most devastating problems affecting a large part of the world’s population. One billion people worldwide are affected by nutritional deficiencies, 800 million people are chronically undernourished, more than 40% of women in the developing world are underweight and/or anemic, and one third of the world’s children are affected by delayed growth and development caused by malnutrition [2]. In the infant and adolescent stages of life, protein-energy malnutrition and vitamin A deficiencies are linked to developmental and growth retardation, increased risk of infection and higher risks of death and blindness [1,2]. Protein-energy malnutrition is the most important deficiency resulting in a higher risk of death, increased risk of infection and a reduced quality of life [1]. Progress during the last twenty years in reducing protein-energy malnourishment among infants and young children has been exceedingly slow, while micronutrient and vitamin deficiency have contributed to worsen the situation [1]
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