Chlamydomonas reinhardtii Raw sequence reads
Nitrogen and phosphorus are essential macronutrients for plant growth and major pollutants driving aquatic eutrophication. Microalgae represent a sustainable biological platform for nutrient recovery and circular utilization from wastewater, yet the molecular mechanisms governing efficient urea assimilation and its coordination with phosphorus uptake remain inadequately characterized. This study investigated how overexpression of the high-affinity urea transporter gene DUR3 enhances nutrient scavenging capacity in the model green alga Chlamydomonas reinhardtii. DUR3-overexpressing (DUR3-OE) lines exhibited concentration-dependent growth responses to urea, with significant promotion at low-to-moderate levels and inhibition under high urea or pure urea conditions. Notably, DUR3-OE consistently elevated chlorophyll content and photosynthetic efficiency (Fv/Fm) across ammonium, urea, and mixed nitrogen regimes. Under mixed nitrogen supply, DUR3-OE lines simultaneously increased cellular nitrogen and phosphorus contents. Except in pure urea medium, engineered strains demonstrated enhanced total phosphorus accumulation and superior phosphorus recovery efficiency from the culture medium. Transcriptomic analysis revealed DUR3 overexpression orchestrates a regulatory network involving nitrogen/phosphorus metabolism, photosynthesis, and carbon transport. RT-qPCR validation confirmed significant upregulation of PMA2, phosphate transporters (PTB3, PTB7), inorganic carbon transporter HLA3, and photosynthesis-related genes, mechanistically explaining the improved nutrient assimilation and photosynthetic performance. These findings establish DUR3 as a key genetic target for engineering microalgae with optimized nitrogen-phosphorus co-uptake capabilities, providing a molecular foundation for developing high-efficiency algal strains in wastewater bioremediation and nutrient circular economy applications.