ASN2 is a key enzyme in asparagine biosynthesis under ammonium sufficient conditions

Abstract

The modification and enhancement of plant amino acid accumulation is potentially beneficial in terms of the production of suitable crop plants for food or feeds, and also with respect to possible environmental improvement via the effective use of nitrogen nutrition. It is also expected that modified plants will produce beneficial nitrogenous compounds, such as proteins, secondary metabolites, or nucleic acids. The size of amino acid pools in plants is strictly controlled by certain environmental factors such as light and nutrition. In order to gain an understanding of the mechanisms that control amino acid biosynthesis and metabolism, we investigated the diurnal changes in amino acid contents and also how the amino acid contents change with the progression of growth. We observed that almost all the amino acids in plant leaves undergo diurnal changes and that the pattern of these changes was different in young and old stages. We focused on correlation of the asparagine content and the expression of ASN2 asparagine synthetase, since under our experimental conditions their fluctuating patterns were found to be similar. The asparagine contents of ASN2-overexpressing and -underexpressing plants were increased and decreased, respectively, when they were grown under normal light and nutrient conditions. These changes in asparagine content were marked when the plants were grown under conditions where ammonium was the sole nitrogen source. It has been previously reported that ASN2 expression and ammonium metabolism are correlated. Our findings and these previous observations suggest that ASN2 functions as a regulator of asparagine biosynthesis and metabolism and that it mediates the effective use of nitrogen under ammonium-sufficient conditions.

Changes in the C/N balance caused by increasing external ammonium concentrations are driven by carbon and energy availabilities during ammonium nutrition in pea plants: the key roles of asparagine synthetase and anaplerotic enzymes

“…In this regard, Wong et al () have established a correlation between Atas2 expression and cellular NH 4 + content in Arabidopsis . Furthermore, AS2 has been proposed to be a regulator of Asn biosynthesis and metabolism and as a mediator in the use of N under NH 4 + ‐sufficient conditions in Arabidopsis (Igarashi et al ). Although as genes may play different roles in various aspects of N metabolism (Wong et al ), the poor homology shown between Psas2 and Atas2 (Gaufichon et al ) makes it difficult to correlate the same function to both enzymes, thus meaning that additional studies are needed.…”

Short-term transcriptomic analysis at organ scale reveals candidate genes involved in low N responses in NUE-contrasting tomato genotypes

“…The ASNS is a key enzyme in the Nmetabolism involved in the hydrolyzation of glutamine to synthesize asparagine, the amino acid with the highest N/C ratio, used as the main stored and transported N form through the vascular tissues in many plants (Lea et al, 2007;Gaufichon et al, 2010;Gaufichon et al, 2013). The ASNS overexpression in Arabidopsis revealed a higher asparagine level in plant tissues together with an increased tolerance to N-deprivation (Lam et al, 2003;Igarashi et al, 2009), suggesting that this may be a good and viable strategy for improving NUE. Accordingly, our results suggested that RO showed a faster induction of these genes after initial downregulation compared to UC82, allowing RO to better withstand N-deficiency.…”

OsASN1 Plays a Critical Role in Asparagine-Dependent Rice Development

“…AtASN1 and AtASN3 showed quite different expression patterns compared with AtASN2 , and these genes are induced by quite different stimuli [15]. The analysis of ASN mutants indicated that AtASN2 plays a role in the primary N assimilation for N storage and export [16,17]. Decades ago, asparagine synthetase was analyzed in rice, and the expression pattern and function were investigated [18,19].…”