Abstract
Ferredoxins (FDX) are final electron carrier proteins in the plant photosynthetic pathway, and function as major electron donors in diverse redox-driven metabolic pathways. We previously showed that overexpression of a major constitutively expressed ferredoxin gene PETF in Chlamydomonas decreased the reactive oxygen species (ROS) level and enhanced tolerance to heat stress. In addition to PETF, an endogenous anaerobic induced FDX5 was overexpressed in transgenic Chlamydomonas lines here to address the possible functions of FDX5. All the independent FDX transgenic lines showed decreased cellular ROS levels and enhanced tolerance to heat and salt stresses. The transgenic Chlamydomonas lines accumulated more starch than the wild-type line and this effect increased almost three-fold in conditions of nitrogen depletion. Furthermore, the lipid content was higher in the transgenic lines than in the wild-type line, both with and without nitrogen depletion. Two FDX-overexpressing Chlamydomonas lines were assessed in a photo microbial fuel cell (PMFC); power density production by the transgenic lines was higher than that of the wild-type cells. These findings suggest that overexpression of either PETF or FDX5 can confer tolerance against heat and salt stresses, increase starch and oil production, and raise electric power density in a PMFC.
Highlights
Photosynthetic microalgae are autotrophic cells that have rapid growth capacity; as such they are key resources in biorefineries [1]
These results indicate that the overexpression of PETF or FDX5 genes enhances the tolerance of Chlamydomonas to heat and salt stresses
These results indicate that both overexpression of PETF and FDX5 can promote oil accumulation in Chlamydomonas in either nitrogen-rich or -starved conditions
Summary
Photosynthetic microalgae are autotrophic cells that have rapid growth capacity; as such they are key resources in biorefineries [1]. To reduce the toxicity of ROS, photosynthetic organisms have evolved several anti-oxidant systems [21] These pathways include enzymes involved in free-radical scavenging, which in turn help relieve the oxidative stress on the cell [14,19]. Overexpression of PETF, the major form of FDX in Chlamydomonas, increased the proportion of reduced ascorbate under normal growth conditions and decreased the ROS level, including H2O2, enhancing the cell survival rate under heat stress [24]. Transgenic Chlamydomonas cell lines overexpressing either PETF or FDX5 were generated to clarify whether increasing gene expression levels of FDXs could alleviate oxidative damage under heat and salt stresses. The two FDX overexpressing Chlamydomonas lines were applied in PMFCs; power density production by the transgenic lines was higher than that for the wild type
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