Abstract
Iron superoxide dismutase 1 (FSD1) was recently characterized as a plastidial, cytoplasmic, and nuclear enzyme with osmoprotective and antioxidant functions. However, the current knowledge on its role in oxidative stress tolerance is ambiguous. Here, we characterized the role of FSD1 in response to methyl viologen (MV)-induced oxidative stress in Arabidopsis thaliana. In accordance with the known regulation of FSD1 expression, abundance, and activity, the findings demonstrated that the antioxidant function of FSD1 depends on the availability of Cu2+ in growth media. Arabidopsis fsd1 mutants showed lower capacity to decompose superoxide at low Cu2+ concentrations in the medium. Prolonged exposure to MV led to reduced ascorbate levels and higher protein carbonylation in fsd1 mutants and transgenic plants lacking a plastid FSD1 pool as compared to the wild type. MV induced a rapid increase in FSD1 activity, followed by a decrease after 4 h long exposure. Genetic disruption of FSD1 negatively affected the hydrogen peroxide-decomposing ascorbate peroxidase in fsd1 mutants. Chloroplastic localization of FSD1 is crucial to maintain redox homeostasis. Proteomic analysis showed that the sensitivity of fsd1 mutants to MV coincided with decreased abundances of ferredoxin and photosystem II light-harvesting complex proteins. These mutants have higher levels of chloroplastic proteases indicating an altered protein turnover in chloroplasts. Moreover, FSD1 disruption affects the abundance of proteins involved in the defense response. Collectively, the study provides evidence for the conditional antioxidative function of FSD1 and its possible role in signaling.
Highlights
Photosynthetic light reactions are accompanied by the formation of reactive oxygen species (ROS) (Pospíšil, 2016; Foyer, 2018)
A previous study has shown that the N-terminal fusion of GFP to FSD1 disturbs the plastid-targeting motif, and the GFP-FSD1 line lacks the plastidic pool of FSD1
The study demonstrated that the abundance and activity of FSD1 in the wild type (WT) and both complemented lines vary inversely with Cu2+ concentration in the growth media
Summary
Photosynthetic light reactions are accompanied by the formation of reactive oxygen species (ROS) (Pospíšil, 2016; Foyer, 2018). Ferredoxin (Fd), the last electron acceptor of PSI, has been reported to produce O2·−; the reduction of O2 by Fd is highly dependent on available NADP+ and is lower than the contribution of O2 reduction by membranebound photosynthetic electron transport chain components (Kozuleva and Ivanov, 2016). Its toxicity is exerted by catalyzing light-dependent electron transfer from PSI to O2, resulting in O2·− production (Chia et al, 1982; Hawkes, 2014). The ROS produced by MV can overcome the cellular protective mechanisms and cause severe damage (Hawkes, 2014). Owing to these characteristics, MV is widely used in plant science as an oxidative stress-inducing agent
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