A lack of genomic information until now hindered understanding of the molecular basis for metal stress response in seaweeds. Therefore, the recent sequencing of the genome for brown alga (Ectocarpus siliculosus) provided the opportunity to address this question. The project 'A toxico-genomic study of the model brown alga Ectocarpus siliculosus' (ECTOTOX) investigated copper toxicity mechanisms in brown algae. In particular, the project studied the expression of genes involved in glutathione (GSH) and phytochelatin (PC) synthesis. PCs are the best understood intracellular ligands in plants and play a crucial role in minimising the detrimental effects of metals. These small sulphur-rich peptides are created through the synthesis of GSH by two different enzymes, which act as an antioxidant within in the cell. Maintaining the equilibrium between synthesis and utilisation of GSH in order to reduce oxidative damage and produce PCs could be critical to combating metal stress. In addition, the toxic effects of metals are associated with reactive oxygen metabolism. Therefore, tolerance to metal stress depends upon systems that involve antioxidant enzymes, to prevent (or at least reduce) oxidative damage. Project partners determined the level of tolerance to copper by measuring growth and photosynthesis in strains of E. siliculosus. The algae were collected from sampling sites with different pollution histories and exposed to a range of metal concentrations. Copper toxicity was also assessed in the spores of brown alga, revealing that this life stage is more copper sensitive than the adult plant, resulting in fewer reproductive organs being formed. Results highlighted the importance of PCs as intracellular metal chelators in brown algae in response to low copper levels. The findings support the use of PCs and related genes (in particular PC synthase) as biomarkers of copper pollution. ECOTOX work has provided new insights into the evolution of metal tolerance and metal-induced defence mechanisms in an ecologically important marine organism. It will also enable environmental protection agencies to develop more sensitive monitoring tools for assessing the health status of coastal waters.
Metal tolerance, seaweed, marine organisms, metal stress response, brown alga, Ectocarpus siliculosus, toxico-genomic, glutathione, phytochelatin, oxidative damage, reactive oxygen metabolism, antioxidant enzymes, phytochelatin synthase, biomarker