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Plant Physiology Preview Published on September 1, 2006; 10.1104/pp.106.085514
Received June 21, 2006 Glutamate:glyoxylate Aminotransferase (GGAT) Modulates Amino Acid Contents during Photorespiration
Institute of Life Sciences, Ajinomoto Co., Inc., Kawasaki 210-8681, Japan * Corresponding author; email: daisuke_igarashi{at}ajinomoto.com.
In photorespiration, peroxisomal glutamate:glyoxylate aminotransferase (GGAT) catalyzes the reaction of glutamate and glyoxylate to produce 2-oxoglutarate and glycine. Previous studies demonstrated that alanine aminotransferase-like protein functions as a photorespiratory GGAT. Photorespiratory transamination to glyoxylate, which is mediated by GGAT and serine glyoxylate aminotransferase (SGAT), is believed to play an important role in the biosynthesis and metabolism of major amino acids. To better understand its role in the regulation of amino acid levels, we produced 42 GGAT1 overexpression lines that express different levels of GGAT1 mRNA. The levels of free serine, glycine, and citrulline increased markedly in GGAT1 overexpression lines compared with levels in the wild-type, and levels of these amino acids were strongly correlated with the levels of GGAT1 mRNA and with the GGAT activity in the leaves. This accumulation began soon after exposure to light and was repressed under high levels of CO2. Light and nutrient conditions both affected the amino acid profiles; supplementation with NH4NO3 increased the levels of some amino acids compared with the controls. The results suggest that the photorespiratory aminotransferase reactions catalyzed by GGAT and SGAT are both important regulators of amino acid contents.
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