Modelling of the heat stress response in Chlamydomonas

Stefan Schmollinger1, Miriam Schulz-Raffelt2, Alexander Skupin1, Daniela Strenkert1, Daniel Veyel1, Olivier Vallon4, Oliver Ebenhöh3, and Michael Schroda1

1) Max Planck Institute of Molecular Plant Physiology, Potsdam-Golm, Germany 2) Institut de Biologie environnementale et de biotechnologie, CEA Cadarache, CNRS/CEA-Aix-Marseille, France 3) Institute of Medical Sciences, University of Aberdeen, Foresterhill, UK 4) Institut de Biologie Physico-Chimique, CNRS/Université Pierre et Marie Curie, Paris, France

When cells are exposed to several different stress conditions they respond by a fast transient induction of stress genes encoding heat shock proteins (HSPs), which mainly are molecular chaperones. At the transcription level this response is mediated by heat shock transcription factors (HSFs). In contrast to higher plants where more than 21 HSFs are known, the unicellular green alga Chlamydomonas reinhardtii encodes only one plant-like HSF which serves as key regulator of the stress response. Hence we choose Chlamydomonas in order to understand fundamental concepts of the stress response in plants. To this end we fed Chlamydomonas cell cultures with different specific inhibitors and monitored resulting RNA and protein kinetics in the stress response. We found a direct correlation between the phosphorylation state of HSF1 and the accumulation of HSP gene transcripts. As revealed by feeding with amino acid analogon Canavanine activation of stress kinase(s) appears to be triggered by the accumulation of unfolded proteins. Feeding with an inhibitor of cytosolic protein synthesis led to an impaired attenuation of the stress response, presumably because synthesis of cytosolic chaperones was abolished. Feeding with specific inhibitors of HSP90s induced a stress response under non stress conditions. To determine the HSF1 targets micro array analysis have been performed. Based on these results a mathematical model has been set up that is able to reproduce the experimental observations.

e-mail address of presenting author: Schmollinger@mpimp-golm.mpg.de