Abstract
Glutamate derived γ-aminobutyric acid (GABA) is synthetized in the cytosol prior to delivery to the mitochondria where it is catabolized via the TCA cycle. GABA accumulates under various environmental conditions, but an increasing number of studies show its involvement at the crossroad between C and N metabolism. To assess the role of GABA in modulating cellular metabolism, we exposed seedlings of A. thaliana GABA transporter gat1 mutant to full nutrition medium and media deficient in C and N combined with feeding of different concentrations (0.5 and 1 mM) of exogenous GABA. GC-MS based metabolite profiling showed an expected effect of medium composition on the seedlings metabolism of mutant and wild type alike. That being said, a significant interaction between GAT1 deficiency and medium composition was determined with respect to magnitude of change in relative amino acid levels. The effect of exogenous GABA treatment on metabolism was contingent on both the medium and the genotype, leading for instance to a drop in asparagine under full nutrition and low C conditions and glucose under all tested media, but not to changes in GABA content. We additionally assessed the effect of GAT1 deficiency on the expression of glutamate metabolism related genes and genes involved in abiotic stress responses. These results suggest a role for GAT1 in GABA-mediated metabolic alterations in the context of the C-N equilibrium of plant cells.
Highlights
Introduction γAminobutyric acid (GABA) was first extracted from plants in the middle of the previous century (Steward et al, 1949)
Increased levels of Glutamate derived γ-aminobutyric acid (GABA) were measured in gat1 under and C and N- deficient media compared to ws, while no changes in the non-protein amino acid were detected between the two genotypes under full nutrition (FN) (Table 1, Figure 2)
Several amino acids permeases have been isolated in Arabidopsis, whose main substrates were glutamate, glutamine and aspartate, with low or no affinity to GABA (Fischer et al, 2002; Meyer et al, 2006)
Summary
Introduction γAminobutyric acid (GABA) was first extracted from plants in the middle of the previous century (Steward et al, 1949). Studies have shown that the key regulatory enzyme of GABA biosynthesis is glutamate decarboxylase (GAD) whose overexpression in transgenic plants significantly reduced the levels of glutamate (Baum et al, 1996; Bouché and Fromm, 2004). This observation suggests that GABA could participate in the regulation of N metabolism and uptake (Forde, 2002) yet raised questions concerning the transport of GABA both within the plant and GAT1-role in carbon-nitrogen balance within the plant cell. We studied the metabolism and gene expression of the Arabidopsis mutant gat, lacking the GABA transporter GAT1, under different C-N media and when supplemented with exogenous GABA
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