Distribution and Functions of Monodehydroascorbate Reductases in Plants: Comprehensive Reverse Genetic Analysis of Arabidopsis thaliana Enzymes

Abstract

Monodehydroascorbate reductase (MDAR) is an enzyme involved in ascorbate recycling. Arabidopsis thaliana has five MDAR genes that encode two cytosolic, one cytosolic/peroxisomal, one peroxisomal membrane-attached, and one chloroplastic/mitochondrial isoform. In contrast, tomato plants possess only three enzymes, lacking the cytosol-specific enzymes. Thus, the number and distribution of MDAR isoforms differ according to plant species. Moreover, the physiological significance of MDARs remains poorly understood. In this study, we classify plant MDARs into three classes: class I, chloroplastic/mitochondrial enzymes; class II, peroxisomal membrane-attached enzymes; and class III, cytosolic/peroxisomal enzymes. The cytosol-specific isoforms form a subclass of class III and are conserved only in Brassicaceae plants. With some exceptions, all land plants and a charophyte algae, Klebsormidium flaccidum, contain all three classes. Using reverse genetic analysis of Arabidopsis thaliana mutants lacking one or more isoforms, we provide new insight into the roles of MDARs; for example, (1) the lack of two isoforms in a specific combination results in lethality, and (2) the role of MDARs in ascorbate redox regulation in leaves can be largely compensated by other systems. Based on these findings, we discuss the distribution and function of MDAR isoforms in land plants and their cooperation with other recycling systems.

Physiological and Differential Proteomic Analysis at Seedling Stage by Induction of Heavy-Ion Beam Radiation in Wheat Seeds

“…Glutathione peroxidase (GPX) and glutaredoxin (GRX) oxidize H 2 O 2 and disulfide (R-S-S-R′) to (H-S-S-R), H 2 O, and GSSG in the presence of GSH ( Xiao et al, 2019 ). The ascorbic acid-glutathione cycle (AsA-GSH) plays the role of “core of redox signaling” in stress-threatened plants and is involved in key processes of hydrogen peroxide metabolism, and its key enzymes include ascorbic acid peroxide (APX) and monodehydroascorbate reductase (MDHAR) ( Foyer and Noctor, 2011 ; Tanaka et al, 2021 ). In response to radiation, wheat seedlings scavenge H 2 O 2 and disulfide P (SSG) through GSH-dependent GPX, GRX, and GS, as well as the ascorbic acid-glutathione cycle.…”

Chloroplastic ascorbate peroxidases targeted to stroma or thylakoid membrane: The chicken or egg dilemma

“…These classes correspond to chloroplastic/mitochondrial, peroxisomal membrane‐bound and cytosolic/peroxisomal isoforms, respectively. In Brassicaceae plants, there is also a subclass of class III, which is correspondent to a cytosol‐specific MDHAR [48]. Although the classification of MDHAR genes is ambiguous, in Rhodophyte and Chlorophyte generally there is only one MDHAR gene of class I, and previous work demonstrated biochemically that MDHAR activity is only in chloroplast fraction of Chlamydomonas sp.…”

Protein-protein interactions in plant antioxidant defense

“…MDARs, enzymes using NADH and NADPH as electron donors compartmentalize into cytosol, chloroplasts, mitochondria, and peroxisomes ( Tanaka et al., 2021 ) and are crucial for plant abiotic and biotic stress responses ( Li et al., 2010 ; Yeh et al., 2019 ). They are regulated on transcriptional and posttranscriptional levels ( Feng et al., 2014 ).…”