Linking phenotypic and transcriptomic traits of diuron exposure and predator response in Chlamydomonas reinhardtii. linking effects

Organisms living in aquatic ecosystems are constantly exposed to multiple stressors,including pollution, habitat degradation and predation. These stressors often act syn-ergistically, but the mechanisms behind these actions are not well understood. In thisstudy, we exposed the single cell green algaChlamydomonas reinhardtiito the herbicideDiuron at environmentally relevant concentrations and to predator cues fromDaphniagaleata, and monitored the dynamics of algal growth, morphology and gene expression.At the phenotype level, we observed a decrease in chlorophyll fluorescence under herbi-cide exposure. At the molecular level, the response to Diuron was larger within 8 daysof exposure (downregulation of glycolysis, protein synthesis, lipid metabolism), whilethe response to predator cues was stronger at later time points (upregulation of the cellcycle, protein metabolism and oxidative stress). The response to the exposure of bothstressors followed the stronger of the two: at early time points it was more similar toDiuron exposure, while at later time points it was more similar to the predator exposure.The response for all treatments was much stronger in the chloroplast encoded genes thanin the nuclear encoded genes and followed completely different trajectories for each ofthe three treaments, suggesting that plastid-based gene expression should be examinedmore carefully when evaluating molecular effects of stressors.