Gene expression induced by copper stress in the diatom Thalassiosira pseudonana

Utilizing a PCR-based subtractive cDNA approach, we demonstrated that the marine diatom Thalassiosira pseudonana exhibits a rapid response at the gene level to elevated concentrations of copper and that this response attenuates over 24 h of continuous exposure. A total of 16 copper-induced genes were identified, 11 of which were completely novel; however, many of the predicted amino acid sequences had characteristics suggestive of roles in ameliorating copper toxicity. Most of the novel genes were not equivalently induced by H2O2- or Cd-induced stress, indicating specificity in response. Two genes that could be assigned functions based on homology were also induced under conditions of general cellular stress. Half of the identified genes were located within two inverted repeats in the genome, and novel genes in one inverted repeat had mRNA levels induced by approximately 500- to 2,000-fold by exposure to copper for 1 h. Additionally, some of the inverted repeat genes demonstrated a dose-dependent response to Cu, but not Cd, and appear to belong to a multigene family. This multigene family may be the diatom functional homolog of metallothioneins.