The In Vitro Interaction of 12-Oxophytodienoic Acid and Related Conjugated Carbonyl Compounds with Thiol Antioxidants

Abstract

α,β-unsaturated carbonyls interfere with numerous plant physiological processes. One mechanism of action is their reactivity toward thiols of metabolites like cysteine and glutathione (GSH). This work aimed at better understanding these interactions. Both 12-oxophytodienoic acid (12-OPDA) and abscisic acid (ABA) conjugated with cysteine. It was found that the reactivity of α,β-unsaturated carbonyls with GSH followed the sequence trans-2-hexenal < 12-OPDA ≈ 12-OPDA-ethylester < 2-cyclopentenone << methyl vinylketone (MVK). Interestingly, GSH, but not ascorbate (vitamin C), supplementation ameliorated the phytotoxic potential of MVK. In addition, 12-OPDA and 12-OPDA-related conjugated carbonyl compounds interacted with proteins, e.g., with members of the thioredoxin (TRX)-fold family. 12-OPDA modified two cysteinyl residues of chloroplast TRX-f1. The OPDAylated TRX-f1 lost its activity to activate the Calvin–Benson-cycle enzyme fructose-1,6-bisphosphatase (FBPase). Finally, we show that 12-OPDA interacts with cyclophilin 20-3 (Cyp20-3) non-covalently and affects its peptidyl-prolyl-cis/trans isomerase activity. The results demonstrate the high potential of 12-OPDA as a diverse interactor and cellular regulator and suggest that OPDAylation may occur in plant cells and should be investigated as novel regulatory mechanism.

Oxylipins and Reactive Carbonyls as Regulators of the Plant Redox and Reactive Oxygen Species Network under Stress

“…Consequently, thiol synthesis is stimulated, strengthening the redox capacity of the cell. This change in redox state in turn alters the expression of 12-OPDA-responsive genes [ 27 , 28 , 96 , 133 ]. Contrary to Cyp20-3 stimulation, OPDAylation diminishes the H 2 O 2 scavenging function of 2-CysPRX [ 133 ].…”

“…This change in redox state in turn alters the expression of 12-OPDA-responsive genes [ 27 , 28 , 96 , 133 ]. Contrary to Cyp20-3 stimulation, OPDAylation diminishes the H 2 O 2 scavenging function of 2-CysPRX [ 133 ]. OPDAylation of TRXs drastically impedes their activity as redox transmitters, thereby decreasing the rate of TRX-dependent Cyp20-3 reduction and glutathione peroxidase (GPXL) regeneration.…”

“…Second, inhibition of chloroplast TRXs also diminishes TRX-dependent FBPase reduction. As a consequence, CO 2 assimilation and starch synthesis are inhibited, reducing the energy consumption by the Calvin–Benson cycle [ 133 ].…”

Organelles and phytohormones: a network of interactions in plant stress responses

“…This redox change then plays a role in the expression of OPDA-dependent genes. By contrast, OPDAylation describes the covalent binding of OPDA to protein thiols ( Maynard et al , 2021 ). Such thiols are targets of multiple post-translational modifications as part of what is called the thiol switch, and OPDAylation could be another player in this regulatory system.…”

OPDAylation of Thiols of the Redox Regulatory Network In Vitro

“…An example for the OPDA function as a ligand is the chloroplast cyclophilin 20-3 (CYP20-3), which upon reversible binding of OPDA associates with the cysteine synthase complex and activates synthesis of O-acetyl-serine from serine, the precursor for cysteine synthesis, by serine acetyltransferase [6]. Reversibility of OPDA association with CYP20-3 independent of thiols was demonstrated by titrating free thiols after incubating CYP20-3 with thiol reactive compounds such as methyl vinylketone and OPDA [7]. While thiols of CYP20-3 were blocked with vinylketone, they remained reactive in the presence of OPDA.…”