Chronological transcriptome changes induced by exposure to cyanoacrylate resin nanoparticles in Chlamydomonas reinhardtii with a focus on ROS development and cell wall lysis-related genes

Abstract

Resin nanoparticles composed of isobutyl cyanoacrylate polymers (iBCA-NPs) are reported to induce acute cell death in many microalgal species. Chronological transcriptome changes induced by exposure to iBCA-NPs in Chlamydomonas reinhardtii (Chlorophyceae) were investigated using next-generation sequencing. Genes encoding antioxidant enzymes, such as glutathione peroxidase (GPX5), Fe-superoxide dismutase (Fe-SOD), and glutathione S-transferase (GSTS1), were prominently upregulated when the cell death ratio reached approximately 3 %. Subsequently, strong expression of these genes was maintained even when the cell death ratio reached ~30 %. Apart from these genes, nine out of 20 heat shock protein (HSP)-coding genes were also upregulated. There was a positive correlation between cell death and ROS accumulation. Upregulation of these genes must be a response to cope with the stresses induced by the ROS accumulation.Cre13.g605200, which is one of 31 genes annotated to encode cell wall hydrolytic enzymes, was highly upregulated by exposure to iBCA-NPs. Three tag-insertion mutants of the Cre13.g605200 gene showed considerably more resistance to cell wall hydrolysis and nanoparticle-induced cell death than the parent strain, suggesting that the Cre13.g605200 gene encodes a cell wall hydrolytic enzyme, and that its upregulation contributes to acute cell death induced by the iBCA-NPs. Positive contribution of the Cre13.g605200 to cell death suggests that the target of nanoparticles (NPs) to induce cell death is located inside the cell walls.The laddering DNA of nucleosome units, a hallmark of programmed cell death (PCD), was barely detectable in the smeared DNA of C. reinhardtii cells exposed to iBCA-NPs. This shows that necrosis-like cell death is the most common type of induced cell death caused by iBCA-NPs exposure. Induced cell death can be the result of intracellular damage to proteins, lipids and DNA caused by ROS.