Enhanced thermotolerance via overexpression of a stromal ascorbate peroxidase in Nannochloropsis oceanica

Overexpression of the heat-responsive ascorbate peroxidase gene NoAPX2430 improves thermotolerance and growth of Nannochloropsis oceanica, offering potential strategies for enhanced resilience in plant cells. Microalgae are promising for industrial lipid production but face challenges from high-temperature (HT) stress. This study focused on improving thermotolerance in Nannochloropsis oceanica by studying and modifying the heat-responsive ascorbate peroxidase gene, NoAPX2430. Functional and localization analyses confirmed NoAPX2430 as an active enzyme in the chloroplast stroma. Knockdown of NoAPX2430 resulted in reduced growth, photosynthetic efficiency, and reactive oxygen species (ROS) scavenging under HT (35 °C). In contrast, overexpression of NoAPX2430 significantly improved photosynthetic performance, lowered ROS levels, and boosted growth rates. Additionally, lipid and triacylglycerol contents increased significantly under combined nitrogen depletion and HT, with polyunsaturated fatty acids rising by up to 194.4%. These results highlight NoAPX2430's critical role in enhancing thermotolerance and lipid biosynthesis. This provides a foundation for genetic and environmental strategies to boost microalgal resilience and productivity for sustainable biofuel and nutraceutical development.