FSD1: developmentally-regulated plastidial, nuclear and cytoplasmic enzyme with anti-oxidative and osmoprotective role.

Although superoxide dismutases (SODs) are prominent superoxide radical (O2 (.-) ) - decomposing enzymes determining plant abiotic stress tolerance, the data on their subcellular localization and developmental expression are elusive. Therefore, we aimed to address the developmental expression, organ-specific, and subcellular localization patterns of iron superoxide dismutase FSD1 in Arabidopsis using advanced fluorescence microscopy methods. We found that fsd1 knockout mutants exhibit reduced lateral root number and that this phenotype was complemented by proFSD1::GFP:FSD1 and proFSD1::FSD1:GFP constructs. Light sheet fluorescence microscopy revealed a temporary accumulation of FSD1-GFP at the site of endosperm rupture during seed germination. In emerged roots, FSD1-GFP showed the highest abundance in cells of the lateral root cap, columella, and endodermis/cortex initials. The largest subcellular pool of FSD1-GFP was localized in the plastid stroma, while it was also located in the nuclei and cytoplasm. FSD1 is crucial for seed germination and salt stress tolerance, which is tightly coupled with FSD1-GFP subcellular relocation to the plasma membrane. It is most likely involved in superoxide decomposition in the periplasm. Plastidial FSD1 pool is required for acquiring full oxidative stress tolerance in Arabidopsis. This study suggests a new osmoprotective function of SODs in plants. This article is protected by copyright. All rights reserved.