Over-expression of a tomato N-acetyl-L-glutamate synthase gene (SlNAGS1) in Arabidopsis thaliana results in high ornithine levels and increased tolerance in salt and drought stresses

Abstract

A single copy of the N-acetyl-L-glutamate synthase gene (SlNAGS1) has been isolated from tomato. The deduced amino acid sequence consists of 604 amino acids and shows a high level of similarity to the predicted Arabidopsis NAGS1 and NAGS2 proteins. Furthermore, the N-terminus ArgB domain and the C-terminus ArgA domain found in SlNAGS1 are similar to the structural arrangements that have been reported for other predicted NAGS proteins. SlNAGS1 was expressed at high levels in all aerial organs, and at basic levels in seeds, whereas it was not detected at all in roots. SlNAGS1 transcript accumulation was noticed transiently in tomato fruit at the red-fruit stage. In addition, an increase of SlNAGS1 transcripts was detected in mature green tomato fruit within the first hour of exposure to low oxygen concentrations. Transgenic Arabidopsis plants have been generated expressing the SlNAGS1 gene under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Three homozygous transgenic lines expressing the transgene (lines 1-7, 3-8, and 6-5) were evaluated further. All three transgenic lines showed a significant accumulation of ornithine in the leaves with line 3-8 exhibiting the highest concentration. The same lines demonstrated higher germination ability compared to wild-type (WT) plants when subjected to 250 mM NaCl. Similarly, mature plants of all three transgenic lines displayed a higher tolerance to salt and drought stress compared to WT plants. Under most experimental conditions, transgenic line 3-8 performed best, while the responses obtained from lines 1-7 and 6-5 depended on the applied stimulus. To our knowledge, this is the first plant NAGS gene to be isolated, characterized, and genetically modified.

Proline Metabolism and Its Implications for Plant-Environment Interaction

“…Less well studied is the acetyl-glutamate pathway which resides in the chloroplast (Figure 4). The importance of this pathway was recently indicated by Kalamaki et al (2009), who cloned (from tomato) the first plant N-acetyl-glutamate synthase (EC 2.3.1.1) and overexpressed it in Arabidopsis. The transgenic plants had elevated levels of ornithine, were more able to germinate in the presence of salt, and soil grown plants were more resistant to salt or soil drying (Kalamaki et al, 2009).…”

“…The importance of this pathway was recently indicated by Kalamaki et al (2009), who cloned (from tomato) the first plant N-acetyl-glutamate synthase (EC 2.3.1.1) and overexpressed it in Arabidopsis. The transgenic plants had elevated levels of ornithine, were more able to germinate in the presence of salt, and soil grown plants were more resistant to salt or soil drying (Kalamaki et al, 2009). Whether or not these plants also had higher amounts of proline was not reported so it is not known whether proline accumulation contributed to the observed stress phenotypes.…”

Metabolite Composition of Grapefruit (<i>Citrus paradisi</i>) Grown in Japan Depends on the Growing Environment and Harvest Period

“…3). In higher plants, ornithine is the precursor of arginine, which serves as a main nitrogen storage compound, and increases in ornithine content induce tolerance to salt and drought stresses (Kalamaki et al, 2009). In addition, ornithine is utilized in the biosynthesis of polyamine, alkaloids, and other plant secondary metabolites (Shargool et al, 1988).…”

Genetic, proteomic and metabolic analysis of the regulation of energy storage in rice seedlings in response to drought

“…Several substances, such as abscisic acid, H 2 O 2 , and NO, have been linked to drought-induced signal transduction [1,2]. Numerous genes, such as SINAGS1 [3], HARDY [4], and RWC3 [5], confer resistance to drought. Many attempts have been made to improve drought resistance in plants through gene transfer [6][7][8][9][10].…”