Monodehydroascorbate Reductase Plays a Role in the Tolerance of Chlamydomonas reinhardtii to Photooxidative Stress

Abstract

Monodehydroascorbate reductase (MDAR; EC 1.6.5.4) is one of the key enzymes in the conversion of oxidized ascorbate (AsA) back to reduced AsA in plants. This study investigated the role of MDAR in the tolerance of Chlamydomonas reinhardtii P.A. Dangeard to photooxidative stress by overexpression and downregulation of the CrMDAR1 gene. For overexpression of CrMDAR1 driven by a HSP70A:RBCS2 fusion promoter, the cells survived under very high-intensity light stress (VHL, 1,800 μmol�m−2�s−1), while the survival of CC-400 and vector only control (vector without insert) cells decreased for 1.5 h under VHL stress. VHL increased lipid peroxidation of CC-400 but did not alter lipid peroxidation in CrMDAR1 overexpression lines. Additionally, overexpression of CrMDAR1 showed an increase in viability, CrMDAR1 transcript abundance, enzyme activity and the AsA: dehydroascorbate (DHA) ratio. Next, MDAR was downregulated to examine the essential role of MDAR under high light condition (HL, 1,400 μmol�m−2�s−1). The CrMDAR1 knockdown amiRNA line exhibited a low MDAR transcript abundance and enzyme activity and the survival decreased under HL conditions. Additionally, HL illumination decreased CrMDAR1 transcript abundance, enzyme activity and AsA:DHA ratio of CrMDAR1-downregulation amiRNA lines. Methyl viologen (an O2�− generator), H2O2 and NaCl treatment could induce an increase in CrMDAR1 transcript level. It represents reactive oxygen species are one of the factor inducing CrMDAR1 gene expression. In conclusion, MDAR plays a role in the tolerance of Chlamydomonas cells to photooxidative stress.

Ascorbate peroxidase 4 plays a role in the tolerance of Chlamydomonas reinhardtii to photo-oxidative stress

“…In wild type, an increase in expression of APX together with MDAR, DHAR, and GR under HL condition demonstrates that ROS over-accumulation and oxidative stress can be effectively prevented via the ascorbate–glutathione cycle. We have previously identified that MDAR 18 , DHAR 19 , and GR 20 are essential for C . reinhardtii to cope with photo-oxidative stress.…”

“…Previously, we identified that monodehydroascorbate reductase (MDAR) 18 , dehydroascorbate reductase (DHAR) 19 , and glutathione reductase (GR) 20 are essential for C . reinhardtii against high light (HL) stress, but the role of APX in high light tolerance is not examined yet.…”

“…Previously, we identified that monodehydroascorbate reductase (MDAR) 18 , dehydroascorbate reductase (DHAR) 19 , and glutathione reductase (GR) 20 are essential for C. reinhardtii against high light (HL) stress, but the role of APX in high light tolerance is not examined yet. Three APX isoforms are found in Chlamydomonas (Phytozome; https ://www.phyto zome.net/), CrAPX1 (Cre02.g087700.t1.2), CrAPX2 (Cre06.g285150.t1.2), and CrAPX4 (Cre05.g233900.t1.2).…”

“…In wild type, an increase in expression of APX together with MDAR, DHAR, and GR under HL condition demonstrates that ROS over-accumulation and oxidative stress can be effectively prevented via the ascorbate-glutathione cycle. We have previously identified that MDAR18 , DHAR19 , and GR20 are essential for C. reinhardtii to cope with photo-oxidative stress. Here, using CrAPX4knockdown amiRNA lines, the HL-induced oxidative damage and cell death when APX activity was depressed supports that APX is also a key factor in C. reinhardtii against HL stress.…”

Characterization and Structural Determination of Cold-Adapted Monodehydroascorbate Reductase, MDHAR, from the Antarctic Hairgrass Deschampsia Antarctica

“…For example, the overexpression of tomato MDHAR, Arabidopsis thaliana MDHAR (AtMDHAR1), and OsMDHAR4 in transgenic plants is associated with an acquired tolerance for abiotic stressors, such as high and low temperatures, ozone, salt, polyethylene glycol, and radiation due to the improvement of redox homeostasis and photosynthesis through the co-activation of cell rescue enzymes [18,33,34]. The homologous MDHAR1 expression of Chlamydomonas reinhardtii increased cell viability by preventing lipid peroxidation given an elevated ascorbate pool under high light-induced oxidative stress, while the downregulation of the gene was associated with a decrease in cell survival due to increased hydrogen peroxide accumulation [35,36].…”