12-Oxophytodienoic Acid Reductase 3 (OPR3) Functions as NADPH-Dependent α,β-Ketoalkene Reductase in Detoxification and Monodehydroascorbate Reductase in Redox Homeostasis

Arabidopsis (Arabidopsis thaliana) 12-oxophytodienoic acid reductase isoform 3 (OPR3) is involved in the synthesis of jasmonic acid by reducing the alpha,beta-unsaturated double bond of the cyclopentenone moiety in 12-oxo-phytodienoic acid (12-OPDA). Recent research revealed that jasmonic acid synthesis is not strictly dependent on the peroxisomal OPR3. The ability of OPR3 to reduce trinitrotoluene suggests that the old yellow enzyme homologue OPR3 has additional functions. Here we demonstrate that OPR3 catalyzes the reduction of a wide spectrum of electrophilic species that share a reactivity towards the major redox buffers glutathione (GSH) and ascorbate (ASC). Furthermore, we demonstrate that 12-OPDA reacts with ascorbate to form an ASC-12-OPDA adduct, but in addition OPR3 has the ability to regenerate ASC from monodehydroascorbate (MDHA). The presented data characterize OPR3 as a bifunctional enzyme with NADPH-dependent alpha,beta-ketoalkene double bond reductase and monodehydroascorbate reductase activities (MDHAR). opr3 mutants exhibited a slightly less reduced ASC pool in leaves in line with the MDHAR activity of OPR3 in vitro. These functions link redox homeostasis as mediated by ASC and GSH with OPR3 activity and metabolism of reactive electrophilic species (RES). © The Author(s) 2019. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.