Extranuclear protection of chromosomal DNA from oxidative stress

Abstract

Eukaryotic organisms evolved under aerobic conditions subjecting nuclear DNA to damage provoked by reactive oxygen species (ROS). Although ROS are thought to be a major cause of DNA damage, little is known about the molecular mechanisms protecting nuclear DNA from oxidative stress. Here we show that protection of nuclear DNA in plants requires a coordinated function of ROS-scavenging pathways residing in the cytosol and peroxisomes, demonstrating that nuclear ROS scavengers such as peroxiredoxin and glutathione are insufficient to safeguard DNA integrity. Both catalase (CAT2) and cytosolic ascorbate peroxidase (APX1) play a key role in protecting the plant genome against photorespiratory-dependent H 2 O 2 -induced DNA damage. In apx1/ cat2 double-mutant plants, a DNA damage response is activated, suppressing growth via a WEE1 kinase-dependent cell-cycle checkpoint. This response is correlated with enhanced tolerance to oxidative stress, DNA stress-causing agents, and inhibited programmed cell death.Arabidopsis | stress tolerance | hydrogen peroxide R eactive oxygen species (ROS) are toxic molecules continuously produced in cells during aerobic metabolism. In plants ROS are produced mainly in peroxisomes during photorespiration, in chloroplasts during photosynthesis, and in mitochondria during respiration (1, 2). Unless detoxified by specialized enzymes and low molecular antioxidants, ROS can lead to protein, lipid, and DNA oxidation and to cell death (1, 2). Plants contain a large network of genes encoding different pathways involved in ROS scavenging and production, with a key role in managing the overall steady-state level of ROS in cells (2). Similar to genotoxic agents or ionizing radiation, ROS-derived DNA oxidation leads to altered bases and damaged sugar residues, resulting in DNA single-and double-strand breaks (3, 4). Strand breaks trigger a DNA damage response (DDR) by inducing the expression of molecular markers associated with DNA damage repair, such as poly(ADP ribose) polymerase (PARP), RAD51, and BREAST CANCER (BRCA) family members (5-8). Upon DNA stress, the ataxia telangiectasia-mutated (ATM) and the ataxia telangiectasia and Rad3-related (ATR) signaling kinases are activated and lead, via the WEE1 serine/ threonine kinase, to a transient cell-cycle arrest that allows cells to repair DNA before proceeding into mitosis (9). Although oxidative DNA base damage has been shown to initiate a DDR in mammalian and yeast cells (10, 11), reports in plants on either the sources of oxidative stress that cause DNA damage or the subsequent induction of a DDR directly through ROS remain scarce (3,12,13). Until now, DNA damage and DDR in plants were studied mainly in response to exogenously applied DNAdamaging agents such as bleomycin and hydroxyurea or ionizing irradiation (9, 14, 15).Protection against damage caused by ROS traditionally has been attributed to enzymes with ROS-detoxifying activities (16), and mutants lacking a particular ROS-scavenging enzyme were considered more sensitive to oxidative stress ...

Cytosolic and Chloroplastic DHARs Cooperate in Oxidative Stress-Driven Activation of the Salicylic Acid Pathway

“…This underscores the potential importance of the cytosolic isoforms in coupling ascorbate and glutathione pools and is consistent with previous studies demonstrating the importance of cytosolic APX1 or GR1 in cat2-triggered responses (Mhamdi et al, 2010a;Vanderauwera et al, 2011) The importance of the cytosol in this context may be related to the peroxisomal location of the H 2 O 2 that becomes available when catalase is deficient, although decreased glutathione oxidation also was reported for single dhar1 and dhar2 mutants after exposure to high light (Noshi et al, 2017). DHAR3 may be more significant in chloroplastic processing, although our data provide little evidence that this isoform plays a specific role in response to paraquat-induced oxidative stress, which largely originates in this organelle (Supplemental Fig.…”

Diastereomer-Specific Uptake, Translocation, and Toxicity of Hexabromocyclododecane Diastereoisomers to Maize

“…41 ROSderived DNA oxidation can lead to both the altered bases and the damaged sugar residues, resulting in DNA single-and double-strand breaks. 19 Although ROS were thought to be a major cause of DNA damage, 42 many studies draw such conclusions solely on the basis of changes of antioxidative enzyme activities, such as those of superoxide dismutase (SOD) and catalase (CAT) in plants, 43 and the direct determination of…”

Accumulation and phytotoxicity of technical hexabromocyclododecane in maize

“…Therefore, the increase in the γ-H2AX level in the present study suggested that DNA damage became more serious with increasing exposure concentration of HBCD. ROS is thought to be a major cause of DNA damage (Vanderauwera et al, 2011). To further confirm whether the DNA damage in maize was induced by U OH generation, sodium benzoate, an U OH scavenger (Chang et al, 2005), was added to the exposure solution.…”