Arabidopsis aldehyde dehydrogenase 10 family members confer salt tolerance through putrescine-derived 4-aminobutyrate (GABA) production

Abstract

Polyamines represent a potential source of 4-aminobutyrate (GABA) in plants exposed to abiotic stress. Terminal catabolism of putrescine in Arabidopsis thaliana involves amine oxidase and the production of 4-aminobutanal, which is a substrate for NAD+-dependent aminoaldehyde dehydrogenase (AMADH). Here, two AMADH homologs were chosen (AtALDH10A8 and AtALDH10A9) as candidates for encoding 4-aminobutanal dehydrogenase activity for GABA synthesis. The two genes were cloned and soluble recombinant proteins were produced in Escherichia coli. The pH optima for activity and catalytic efficiency of recombinant AtALDH10A8 with 3-aminopropanal as substrate was 10.5 and 8.5, respectively, whereas the optima for AtALDH10A9 were approximately 9.5. Maximal activity and catalytic efficiency were obtained with NAD+ and 3-aminopropanal, followed by 4-aminobutanal; negligible activity was obtained with betaine aldehyde. NAD+ reduction was accompanied by the production of GABA and β-alanine, respectively, with 4-aminobutanal and 3-aminopropanal as substrates. Transient co-expression systems using Arabidopsis cell suspension protoplasts or onion epidermal cells and several organelle markers revealed that AtALDH10A9 was peroxisomal, but AtALDH10A8 was cytosolic, although the N-terminal 140 amino acid sequence of AtALDH10A8 localized to the plastid. Root growth of single loss-of-function mutants was more sensitive to salinity than wild-type plants, and this was accompanied by reduced GABA accumulation.

The ALDH21 gene found in lower plants and some vascular plants codes for a NADP+‐dependent succinic semialdehyde dehydrogenase

“…4.1.1.15) in the cytosol. An alternative pathway from polyamines to GABA is catalyzed by copper‐containing amine oxidases (Fincato et al ., ; Planas‐Portell et al ., ) and/or FAD‐dependent amine oxidases followed by aminoaldehyde dehydrogenases (ALDH10 family; Tylichová et al ., ; Kopečný et al ., ; Zarei et al ., ). Once GABA enters mitochondria, it is converted to SSAL via a GABA transaminase (GABA‐T; E.C.…”

Metabolic diversification of nitrogen‐containing metabolites by the expression of a heterologous lysine decarboxylase gene in Arabidopsis

“…Arabidopsis does not produce 5‐aminopentanal or 5‐aminopentanoate but rather produces analogs that are one carbon atom shorter: 4‐aminobutanal and GABA, respectively. The conversion of 4‐aminobutanal to GABA was previously shown to be catalyzed by AtALDH10A8 and AtALDH10A9 (Missihoun et al ., ; Stiti et al ., ; Zarei et al ., ). In this study, we functionally characterized AtALDH10A8 and AtALDH10A9 enzymes and showed that both enzymes could catalyze the conversion of 5‐aminopentanal to 5‐aminopentanoate.…”

“…The full-length cDNA clones of AtALDH10A8 and AtALDH10A9 were obtained from RIKEN BioResource Research Center (https://ja.brc.riken.jp) (pda07810 and pda01165, respectively). Vector construction and the expression of recombinant protein followed by affinity purification were conducted as described previously (Zarei et al, 2016). The reaction mixture for the AtALDH10A8 functional assay consisted of 30 mM Tris-HCl buffer (pH 8.5), 0.1 mM NAD + and 1 mM 5-aminopentanal, whereas the reaction mixture for AtALDH10A9 functional characterization contained 30 mM N-cyclohexyl-2aminoethanesulfonic acid buffer (pH 9.5), 0.5 mM NAD + and 1 mM 5-aminopentanal.…”

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“…It has been also reported that ataldh10A8 and ataldh10A9 T-DNA-insertion mutants reduced GABA accumulation than wild-type plants of A. thaliana during salinity treatment and are more sensitive to salinity stress. [33] GABA-T and GAD are the key enzymes in GABA-shunt pathway. Enzymes activities of these enzymes were assayed at different leaf developmental stages in wild-type and pop2-3 mutant plant and compared with GABA-T complement plant.…”