Functional Genomics Screening in Chlamydomonas reinhardtii Maps the Genetic Landscape of Tolerance to Paraquat and...

Functional genomics offers a powerful, unbiased approach to elucidating the molecular mechanisms underlying the toxicity of environmental pollutants. In this study, we applied genome-wide screening in Chlamydomonas reinhardtii to investigate two classical herbicides: paraquat and diuron. Our screen successfully uncovered critical nuclear-encoded pathways that govern susceptibility. For both herbicides, we identified genes regulating the assembly and maintenance of the photosynthetic machinery, highlighting the central role of nuclear control over these chloroplast-localized targets. Beyond these target-related factors, we discovered novel nontarget-site resistance mechanisms. For paraquat, we identified intracellular trafficking as the central determinant of toxicity, experimentally characterizing a P5B ATPase transporter and a fatty acid elongation pathway whose disruption, we propose, converges on the same endomembrane delivery route through sphingolipid depletion. In contrast, our screening data suggest that diuron tolerance may be associated with a metabolic strategy focused on energy conservation, where the inactivation of specific NADPH-consuming enzymes could preserve reducing power for essential antioxidant defense. Collectively, these findings demonstrate that functional genomics can reveal novel, complex modes of action even for well-characterized chemicals, providing the mechanistic resolution required to advance modern ecotoxicological risk assessments.