Heat shock protein genes in the green alga Tetraselmis suecica and their role against redox and non-redox active metals.

Microalgae are capable of tolerating variations in water temperature and sudden exposures to toxic substances, and cellular heat shock proteins (HSPs) help to protect cells from such stress. Here, we determined the complete open reading frames (ORF) of small TsHSP20 and large TsHSP70 and 100 in the chlorophyte Tetraselmis suecica, and examined the expression levels of these genes after exposure to thermal stressors, redox-active metals, and non-redox-active metals. Putative TsHSP20, TsHSP70, and TsHSP100 proteins had conserved HSP-family motifs with different C-terminus motifs. Phylogenetic analyses of individual HSPs showed that T. suecica clustered well with other chlorophytes. Real-time PCR analysis showed that thermal stress did not significantly change the expression of all the tested TsHSPs. In addition, TsHSP20 showed little gene expression after being exposed to copper, whereas TsHSP70 and 100 genes greatly responded to the redox-active metals in CuSO4 followed by CuCl2, but not to the non-redox active metals. Redox-active metals strongly affected the physiology of the cells, as judged by cell counting, reactive oxygen species imaging and photosynthetic efficiency. These findings suggest that small and large HSPs are differentially involved in the response against environmental stressors. Moreover, metal toxicity may be specifically controlled by the anions in the metal compounds.