Food safety: Structure and expression of the asparagine synthetase gene family of wheat

Asparagine is an important nitrogen storage and transport molecule, but its accumulation as a free amino acid in crops has implications for food safety because free asparagine is a precursor for acrylamide formation during cooking and processing. Asparagine synthesis occurs by the amidation of aspartate, catalysed by asparagine synthetase, and this study concerned the expression of asparagine synthetase (TaASN) genes in wheat. The expression of three genes, TaASN1-3, was studied in different tissues and in response to nitrogen and sulphur supply. The expression of TaASN2 in the embryo and endosperm during mid to late grain development was the highest of any of the genes in any tissue. Both TaASN1 and TaASN2 increased in expression through grain development, and in the grain of field-grown plants during mid-development in response to sulphur deprivation. However, only TaASN1 was affected by nitrogen or sulphur supply in pot-based experiments, showing complex tissue-specific and developmentally-changing responses. A putative N-motif or GCN4-like regulatory motif was found in the promoter of TaASN1 genes from several cereal species. As the study was completed, a fourth gene, TaASN4, was identified from recently available genome data. Phylogenetic analysis showed that other cereal species have similar asparagine synthetase gene families to wheat.