Unlike plants and animals, the phytoflagellate
Euglena gracilis lacks catalase and contains a non-selenocysteine glutathione peroxidase-like protein (EgGPXL), two peroxiredoxins (EgPrx1 and EgPrx4), and one ascorbate peroxidase in the cytosol to maintain reactive oxygen species (ROS) homeostasis. In the present study, the full-length
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Unlike plants and animals, the phytoflagellate
Euglena gracilis lacks catalase and contains a non-selenocysteine glutathione peroxidase-like protein (EgGPXL), two peroxiredoxins (EgPrx1 and EgPrx4), and one ascorbate peroxidase in the cytosol to maintain reactive oxygen species (ROS) homeostasis. In the present study, the full-length cDNA of three cytosolic EgGPXLs was obtained and further characterized biochemically and functionally. These EgGPXLs used thioredoxin instead of glutathione as an electron donor to reduce the levels of H
2O
2 and
t-BOOH. The specific peroxidase activities of these enzymes for H
2O
2 and
t-BOOH were 1.3 to 4.9 and 0.79 to 3.5 µmol/min/mg protein, respectively. Cytosolic
EgGPXLs and
EgPrx1/
EgPrx4 were silenced simultaneously to investigate the synergistic effects of these genes on the physiological function of
E. gracilis. The suppression of cytosolic
EgGPXL genes was unable to induce any critical phenomena in
Euglena under normal (100 μmol photons m
−2 s
−1) and high-light conditions (350 μmol photons m
−2 s
−1) at both autotrophic and heterotrophic states. Unexpectedly, the suppression of
EgGPXL genes was able to rescue the
EgPrx1/EgPrx4-silenced cell line from a critical situation. This study explored the potential resilience of
Euglena to ROS, even with restriction of the cytosolic antioxidant system, indicating the involvement of some compensatory mechanisms.
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