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

Abstract

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.

Durum Wheat Roots Adapt to Salinity Remodeling the Cellular Content of Nitrogen Metabolites and Sucrose

“…Three out of four isoforms of Asn present in wheat (Gao et al, 2016) were considered ( TdAsn1, TdAsn2, and TdAsn3 ), using three different primer pairs, because they can be up-regulated by nitrogen and/or salt stress (Wang et al, 2005; Antunes et al, 2008; Gao et al, 2016). The three isoforms were expressed in all treatments.…”

“…The decrease of glutamate could depend on its use as nitrogen donor in biosynthetic transamination for the production of amides, in particular asparagine which strongly increased in salt stressed HNR (Forde and Lea, 2007) (Table 2, Figures 2G, 3). The increase of asparagine was probably due to a de novo synthesis catalyzed by the isoforms of asparagine synthetase TdAsn1 and TdAsn3 , which were strongly induced by simultaneous salinity and high levels of nitrogen metabolites (e.g., glutamine and glutamate; Lam et al, 1994; Wang et al, 2005; Lea et al, 2007; Gao et al, 2016). In particular, a very strong correlation was found between TdAsn1 , AS, and asparagine ( r ≥ 0.92; P < 0.001).…”

“…RT-PCR was performed in a total volume of 50 μl containing 300 ng of the first strand cDNA reaction products, 5 μl of FastStart Buffer with 20 mM MgCl 2 , 0.2 mM deoxynucleotides, 50 pmol of primers (Table S1), and 2 U of FastStart Taq DNA polymerase (Roche). RT-PCR analysis was performed using gene-specific primers for Asn1, Asn2 , and Asn3 isoforms (Wang et al, 2005; Gao et al, 2016), NR (Carillo et al, 2005; Wang et al, 2005), and degenerate primers for P5CS (Woodrow et al, 2016) (Table S1). The amount of TdAsn1, TdAsn2, TdAsn3, TdNR , and TdP5CS templates mRNA levels were based on the comparison with the level of the 190 bp mRNA for actin (Woodrow et al, 2010), a constitutively expressed “house-keeping” gene.…”

“…For this reason, the potassium to sodium ratio is more critical than the absolute amount of sodium for the cell performance under salinity (Maathuis and Amtmann, 1999; Shabala and Cuin, 2008; Cuin et al, 2009). However, exposure to salinity triggers specific strategies for cell osmotic adjustment and control of ion and water homeostasis to minimize stress damage and to re-establish growth (Hasegawa et al, 2000; Puniran-Hartley et al, 2014; Gao et al, 2016; Woodrow et al, 2016). A ubiquitous mechanism that plants have evolved to adapt to salinity involves sodium sequestration in the vacuole, as a cheap osmoticum, and synthesis and accumulation of compatible compounds, which have a much higher cost in terms of energy needed for their synthesis (50–70 moles ATP for mole), both for osmotic adjustment and oxidative stress protection in the cytosol (Raven, 1985; Cuin et al, 2009; Shabala, 2013).…”

Reducing the acrylamide‐forming potential of wheat

“…This is reflected to some extent in the expression of asparagine synthetase genes (Gao et al. ). There are four asparagine synthetase genes in wheat, TaASN1‐4 (Gao et al.…”