Nanotechnology currently undergoes a rising development partly due to the increasing use of carbon-based nanoparticles, such as Few Layer Graphene (FLG). Owing to their numerous applications, their industrial production is likely to lead to environmental release, including into aquatic ecosystems. In this study, a transcriptomic approach was used to assess the effect of FLG at low (0.1 mg.L-1) and high (50 mg.L-1) concentration on the benthic freshwater diatom Nitzschia palea after 48h of exposure. Direct contact with FLG and induced shading were distinguished to compare the transcriptomic responses. Differentially expressed genes between each exposure and control conditions were identified and their functional description was discussed. Slight transcriptomic response related to cell wall repair was observed in diatoms exposed to low FLG concentration. Exposure to high FLG concentration induced a strong response involving 1907 transcripts. Notably, 16 transcripts involved in chlorophyll biosynthesis process were under-expressed (Log2FoldChange between -3 and -1.2),suggesting a down-regulation of photosynthetic metabolism. Diatoms exposed to high FLG concentration over-expressed about 13 transcripts encoding for extracellular proteins playing a role in cellular adhesion, and two highly up-regulated transcripts involved in cell wall repair. Light deprivation caused by shading induced a down-regulation of genes involved in the energetic metabolism of N. palea. Overall, these results revealed that metabolic pathways impacted by FLG exposure were concentration contact-dependent. Moreover, this study suggests that low FLG concentration, close to environmental conditions, will have minor impact on diatom biofilms whereas high FLG concentration, mimicking accidental release, might be critical for ecosystems.< Réduire