Transcriptional profiling of antioxidant defense system and heat shock protein (Hsp) families in the cadmium- and copper-exposed marine ciliate Euplotes crassu.

To understand the transcriptional response of antioxidant defense system and heat shock protein (Hsp) families of the marine ciliate Euplotes crassus, we analyzed the transcriptome profile using RNA-seq technology after exposure to cadmium (Cd) and copper (Cu). De novo sequence assembly produced 61,240 unigenes with 21,330 BLAST hits and showed high sequence orthology with transcriptomes of other ciliates. Gene annotation and gene ontology (GO) comparison revealed that E. crassus expressed highly diversified but conserved stress-responsive gene families of the antioxidant defense system and Hsps. After waterborne exposure to 250 μg/L of Cd and 25 μg/L of Cu, transcriptional responses of the gene families were significantly modulated, suggesting that even the unicellular E. crassus has a conserved molecular defense mechanism, such as modulating mRNA expression, for homeostasis. These transcriptional responses make E. crassus a potential model for understanding the molecular response of single cell ciliates to heavy metal contamination.