α-Aminoadipic acid metabolism is controlled by the glutathione-dependent redox environment in Arabidopsis

Abstract α-Aminoadipic acid (Aaa) is an intermediate product in the Lys catabolism, on the saccharopine pathway. Since Lys content was increased by various abiotic stress factors affecting the redox environment, a glutathione-dependent redox regulation of the Aaa metabolism was assumed which was not tested earlier. The effect of the modified size and redox state of glutathione pool (reduced + oxidised, GSH + GSSG) on the Aaa content and related amino acid and transcript levels was compared in the wild-type Col-0 plants and the GSH-deficient pad2-1 Arabidopsis mutant with and without (control) treatment. Modification of the size and redox state of glutathione pool resulted in the alteration of Lys, Glu, Pro and Aaa contents and the transcription of the three investigated genes of the saccharopine pathway. Both the Aaa content and the expression of the two genes encoding enzymes of its synthesis (ketoglutarate reductase/saccharopine dehydrogenase, LKR/SDH; aminoadipic semialdehyde dehydrogenase, AASADH) was lower in the pad2-1 mutant, and these parameters, together with the GSSG content, were increased by GSH treatment both in Col-0 and mutant plants. The GSSG content and its ratio in the glutathione pool exhibited a positive correlation with the Aaa content and the transcription of the two genes of its synthesis and the Aaa catabolic gene (dihydrolipoamide-succinyltransferase), which indicates a GSH-dependent control of Aaa metabolism. This latter process in turn can affect the redox environment and stress response because of the NADPH use/formation in its several steps.