Citation:

Reichman, J., C. Rico, B. Smith, H. Ren, A. Fisher, M. Plocher, M. Storm, G. King, AND C. Andersen. Transgenerational changes in Arabidopsis tsRNA expression and chloroplast genomic methylation following exposure to CeO2 nanoparticles. SETAC North America 42nd Annual Meeting, Portland, OR, November 14 - 18, 2021.

Impact/Purpose:

Engineered nanoparticles (ENMs) have been recognized as valuable components of new technologies and are currently being used in a variety of consumer products due to their unique physical, chemical, and electrical properties.  The properties that make these particles functionally unique also may influence their toxicity to organisms in ecosystems.  CSS’s Emerging Materials research is designed to identify potential adverse effects of these materials in the environment, including identification of molecular initiating events (MIE) that may lead to predictable downstream effects and subsequent adverse outcome pathway (AOP) development.  The vast majority of previous studies characterizing the effects of ENMs have reported impacts to organisms within the same generation in which they were exposed. Here, Arabidopsis plants were grown for 3 generations, ± CeO2 ENM treatments during the 1st and 2nd generation. Leaves were sampled from mature 2nd and 3rd generation plants for small RNA sequencing and reduced representation bisulfite sequencing respectively. Significantly regulated transcripts were primarily 5’ transfer-derived small RNAs, which can potentially inhibit translation. Also, differential methylation of cytosines occurred mostly within the Arabidopsis chloroplast genome, possibly impacting ATP synthesis, electron transport and photosystem II.  Overall, this report identifies important biochemical changes downstream of the MIE. Results from both experiments suggest that ENM exposure during the 1st generation attenuated the developmental and molecular responses to a follow-on exposure in the second generation.

Description:

Crops and wild plants are being exposed to increasing amounts of engineered cerium oxide nanoparticles (CeO2-NPs) through soil, water, and air. Recent studies showed that exposure to CeO2-NPs can alter the transcriptome profiles of plants. To further identify transgenerational molecular impacts from exposure, experimental groups of Arabidopsis thaliana plants were grown for three generations. Treatments with 15 mL of 500 mg/L CeO2-NP +/- treatments occurred in the 1st and 2nd generations (C1C2 = control both generations; T1C2 = treated 1st generation; C1T2 = treated 2nd generation; T1T2 = treated both generations).  No treatments were applied during the 3rd generation. Leaves from 28-day-old 2nd and 3rd generation plants were sampled (N = 5) for small RNA sequencing and reduced representation bisulfite sequencing, respectively. Differentially expressed transcripts were predominantly tRNA-derived small RNAs (tsRNA) that were cleaved within the anti-codon loop, and which are capable of regulating translation. For T1C2 plants there was significant up-regulation of 5′ tRH-Asp-GTCs, whereas C1T2 had up-regulation of 5′ tRH-Gly-GCCs. Interestingly, for T1T2 plants there was a switch to down-regulation of 5′ tRH-Gly-GCCs.  We used 124,208 100-CpG probes to quantitate differential methylation at genes across the genomes of 3rd generation plants. Notably, 84% of the genes with differentially methylated CpGs were in the chloroplast genome, while only 3% of all 100-CpG probes were generated there. The most wide-spread enrichments of gene ontologies across treatments were those related to ATP synthesis, electron transport and photosystem II. The most frequently impacted biochemical pathway was also ATP synthesis. Overall, these results point to development of epigenetic memory of particular CeO2-NP exposures that occurred in prior generations. The tsRNA expression was more sensitive to exposures in just the 1st or 2nd generations (T1C2 and C1T2). By contrast, 2nd generation exposures (C1T2 and T1T2) had the largest effect on genomic DNA methylation of 3rd generation plants. Results from these experiments suggest that CeO2 exposure during the 1st generation attenuated the responses to a follow-on exposure in the 2nd generation.

Record Details: