Distinct mRNA and miRNA responses in Chlamydomonas reinhardtii reveal particle-specific adaptive mechanisms to ZnO nanoparticles and ZnO bulk

Abstract

We investigated the adaptive responses of Chlamydomonas reinhardtii to ZnO nanoparticles (ZnO NPs) and ZnO bulk (ZnO Bulk) using integrated physiological, transcriptomic, and miRNA analyses. Cryo-TEM and AAS showed that ZnO NPs accumulated at higher levels and were more widely distributed in cells, whereas ZnO Bulk formed larger intracellular structures. Both materials activated oxidative stress defenses and metal homeostasis, but Bulk uniquely induced strong DNA repair, protein folding, and cell cycle pathways, indicating sustained cellular stress. Small RNA profiling revealed broader miRNA modulation under Bulk exposure, targeting genes linked to chromatin regulation, signaling, and stress adaptation. However, the absence of consistent inverse miRNA–mRNA correlations suggests that miRNAs act mainly as modulators, with transcriptional and proteomic reprogramming driving the primary response. These findings highlight how particle size and aggregation state shape both transcriptional and post-transcriptional regulation in algal stress adaptation, providing new insight into microalgal resilience to engineered ZnO materials.