Methionine Metabolism in Plants
Methionine is a nutritionally essential, sulfur-containing amino acid whose low level in plants diminishes their value as a source of dietary protein for humans and animals. Methionine is also a fundamental metabolite in plant cells since through its first metabolite, S-adenosylmethionine (SAM), it controls the level of several key metabolites such as ethylene, polyamines, and biotin. SAM is also the primary methyl group donor that regulates different processes in plants. Despite its nutritional and regulatory significance, the factors regulating its synthesis and catabolism in plants are not fully known. Moreover, although methionine-associated metabolites play a major role in plant metabolism and growth, only little is known about how the methionine metabolism interacts with other metabolic networks regulating different processes in plants. In recent years, genetic molecular biology techniques have been used to increase and decrease the expression levels of several genes encoded to enzymes in the methionine metabolism. In this review, we summarize recent progress made in the molecular characterization of these genes. We also focus on specific examples where a deeper understanding of the regulation of metabolic networks in plants is needed for a tailor-made improvement of the methionine metabolism, with minimal interference in plant growth and productivity. We describe several different manipulations of methionine metabolism pathways and their effects on plant methionine content. These studies have resulted in the identification of steps important for the regulation of flux through the pathways and for the production of transgenic plants having increased free and protein-bound methionine. Similarly, the expression of methionine-rich storage proteins has resulted in significant improvements in methionine level of some target plant organs. These molecular approaches have provided new insights into the control of methionine level in plants and, in many cases, have resulted in significant improvements in the nutritional value of plants.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © 2008. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, 5585 Guilford Road, Madison, WI 53711-5801, USA. Sulfur: A Missing Link between Soils, Crops, and Nutrition. Agronomy Monograph 50.