Recent advances in asparagine metabolism

Asparagine is a key compound in the nitrogen metabolism of plants. It acts as a major form of nitrogen storage and transport to sink tissues. In the past 20 years, tremendous progress has been made in our understanding of the enzymology of asparagine metabolic pathways and of the biological role of asparagine metabolic enzymes in higher plants, by using a variety of approaches, ranging from protein crystallography to the use of mutants and overexpression lines in combination with molecular analysis and metabolite profiling. Most of the genes and
enzymes involved in asparagine metabolism have been identified and characterized, including asparagine synthetase, β-cyanoalanine nitrilase/hydratase, asparaginase, serine:glyoxylate aminotransferase, and ω-amidase. In leaf, asparagine biosynthesis by asparagine synthetase is stimulated in the dark, a situation associated with carbon deficit. Asparagine appears to participate in photorespiration, providing an input of nitrogen to balance an output of serine or glycine to other pathways. Manipulating asparagine biosynthesis and degradation can alter seed development and composition, and has been used to mitigate the problem of acrylamide formation in food. There is an apparent positive association between the levels of asparagine present in reproductive organs and seed protein accumulation. This chapter presents a perspective on the field of asparagine metabolism, highlighting possible areas of future investigation.