Molecular characterization and expression analysis of copper-zinc superoxide dismutases from the freshwater alga Closterium ehrenbergii under metal stress

摘要

Superoxide dismutase (SOD) acts as the first line of defense against reactive oxygen species (ROS) within cells.In the present study,we determined two novel CuZnSOD genes (designated as CeCSDl and CeCSD2) from the toxicity-testing freshwater algae Closterium ehrenbergii and examined their structural features,phylogenetic relationships,and gene expression under exposure to different metals.Putative CeCSD1 (204 aa,20.6 kDa) and CeCSD2 (155 aa,15.3 kDa) proteins had conserved CuZnSOD family motifs and metal (Cu,Zn) binding sites,but different N-terminus structures,that is,CeCSDl has a signal peptide to chloroplasts.Phylogenetic analysis of each protein revealed that C.ehrenbergii was well clustered with other green algae and plants.Real-time PCR results showed that the gene expression obviously increased with heavy metal exposure.In addition,excess copper considerably increased the SOD activity and ROS generation but decreased the photosynthetic efficiency in treated cells.These results suggest that CeCSDs are involved in the antioxidant defense system and can be regarded as potential biomarkers for monitoring metal contaminants in aquatic environments.