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The genetic basis of adpatation to environmental stress in the ciliate Paramecium caudatum

Mr Joshua Priam Killeen
Kaltz team - University of Montpellier, France
Berendonk team - Institute for Hydrobiology, Dresden, Germany
Sunday, May 18, 2014 to Saturday, May 31, 2014

The range of environmental conditions in which an organism can persist, termed a niche, evolves as organisms adapt. It is expected that a niche will either shift in optimum while maintaining breadth, to match the new range of the environment, or that the niche will broaden, allowing persistence at a greater range of that environmental condition, but with reduced overall performance. This is a widespread assumption, formalised as the trade-off between specialists and generalists. We have investigated the nature of the evolutionary response to environmental change, in the form of temperature stress, in the ciliate Paramecium caudatum by maintaining selection lines for approximately 600 generations at 23 °C (permissive growth conditions) and 32 °C (stress conditions). Using growth rate assays it is apparent that selection lines at high temperature have adapted to their new environment and now survive for longer when subjected to a heat-shock treatment (35 °C). Linking this phenotypic data to gene expression data is our aim, in order to better understand the mechanism by which this adaptation occurred.

Therefore the aim of this STSM was to carry out heat-shock protein (HSP) gene expression assays on these selection lines and their ancestral cultures. The 70 kDa heat-shock proteins (Hsp70s) are a widespread and conserved mechanism for adaptation to temperature stress. Sascha Krenek has previously investigated the importance of a number of HSP genes using real-time quantitative PCR (qPCR). We therefore predicted that there may be a detectable difference in the expression of constitutive or facultative HSP genes. During this STSM we carried out RNA extractions from samples taken from out selection lines and converted these to cDNA by reverse transcription for use in qPCR. We successfully conducted qPCR on a number of selection lines, allowing us to gain a first look at any potential change in HSP expression. We used two reference genes, GAPDH and EF-1α, for normalisation and investigated the expression of two cytosolic HSP genes – CyA (constitutive expression) and CyB (induced expression). We found that heat-shock had a clear effect on the expression of these Hsp70 genes and therefore aim to further investigate the details of this up-regulation using further selection lines to achieve the most robust results possible.



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