γ-Aminobutyrate transaminase limits the catabolism of γ-aminobutyrate in cold-stressed Arabidopsis plants: insights from an overexpression mutant

We tested the hypothesis that γ-aminobutyrate transaminase (GABA-T) regulates the supply of succinate semialdehyde for succinate semialdehyde dehydrogenase or NADPH-dependent glyoxylate/succinate semialdehyde reductase 1 (GLYR1) during stress. Constitutive overexpression (OX) lines of GABA-T were generated in Arabidopsis via the floral-dip method for Agrobacterium-mediated transformation. Polymerase chain reaction enabled selection of four transgenic lines with higher GABA-T transcript levels than the wild-type (WT), but assay of cell-free leaf extracts revealed that only OX1 had elevated GABA-T activity. Brief cold treatments (4 °C exposure for 20 min or 1 h in the dark) increased leaf GABA concentrations in both the WT and OX1, but the concentrations in OX1 were consistently lower. These findings confirm that GABA-T limits the catabolism of GABA when its production is stimulated by stress, and suggest a bioengineering strategy for improving the availability of succinate semialdehyde for the Krebs cycle ...