Abstract
The phosphorylated pathway of serine biosynthesis represents an important pathway in plants. The pathway consist of three reactions catalyzed by the phosphoglycerate dehydrogenase, the phosphoserine aminotransferase and the phosphoserine phosphatase, and the genes encoding for all enzymes of the pathway have been identified. Previously, the importance of the phosphoglycerate dehydrogenase and phosphoserine phosphatase for plant metabolism and development has been shown, but due to the lack of T-DNA insertion mutants, a physiological characterization of the phosphoserine aminotransferase is still missing. Hence, we generated silencing lines specifically down-regulated in the expression of the major PSAT1 gene. The morphological characterization of the obtained PSAT1-silenced lines revealed a strong inhibition of shoot and root growth. In addition, these lines are hypersensitive to the inhibition of the photorespiratory serine biosynthesis, when growing the plants at elevated CO2. Metabolic analysis of PSAT1-silenced lines, showed a strong accumulation of certain amino acids, most likely due to an enhanced ammonium assimilation. Furthermore, phenotypic analysis under low and high-light conditions and in the presence of sucrose revealed, that the phosphorylated pathway of serine biosynthesis is essential for light and sugar-dependent growth promotion in plants.
Highlights
Serine is an important intermediate in various metabolic pathways in plant metabolism, including photorespiration, the biosynthesis of phospholipids, the one-carbon metabolism and the synthesis of amino acids, such as glycine, methionine, cysteine, and tryptophan (Vance and Steenbergen, 2005; Rebeille et al, 2007; Krueger et al, 2009; Tzin and Galili, 2010)
Identification and Expression Patterns of phosphoserine aminotransferase (PSAT) Genes in Arabidopsis thaliana Two genes, PSAT1 (At4g35630) and PSAT2 (At2g17630) with a high similarity to the SERC gene from Escherichia coli, the CCDS6659 gene from Homo sapiens and the YOR184W gene from Saccharomyces cerevisiae were identified in the Arabidopsis thaliana genome (Figure 2)
The presence of PSAT activity in plants has been described previously by several studies (Larsson and Albertsson, 1979; Reynolds et al, 1988) and the gene encoding for the PSAT enzyme has been cloned from spinach and Arabidopsis (Saito et al, 1997; Ho et al, 1998)
Summary
Serine is an important intermediate in various metabolic pathways in plant metabolism, including photorespiration, the biosynthesis of phospholipids, the one-carbon metabolism and the synthesis of amino acids, such as glycine, methionine, cysteine, and tryptophan (Vance and Steenbergen, 2005; Rebeille et al, 2007; Krueger et al, 2009; Tzin and Galili, 2010). Serine is synthesized by two pathways, the phosphorylated pathway of serine biosynthesis (PPSB), and the gluconeogenic pathway (Pizer, 1963; Snell, 1984; Melcher and Entian, 1992; Achouri et al, 1997; Dey et al, 2005). In most other organisms, such as mammals, algae and bacteria, serine is mainly synthesized by the PPSB (Pizer, 1963; Snell, 1984; Melcher and Entian, 1992; Achouri et al, 1997; Dey et al, 2005). More than 70% of the serine synthesized by the photorespiration is recycled by the serine glyoxylate aminotransferase reaction to feed back the carbon into the Calvin cycle and only 30% is used to satisfy the demand of serine for other cellular processes (Busch et al, 2018)
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