Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/22905
How do organisms react to a warming environment? How do such environmental changes affect species interactions? These are key questions in times of global warming. One strategy of coping with environmental changes is acclimatization. Therefore, species evolved complex molecular stress-response mechanisms including heat-shock systems (protein repair) and DNA repair pathways. Here, we analyzed candidate gene expression in the lichen fungus Peltigera membranacea and its cyanobacterial Nostoc symbiont, a key player in carbon and nitrogen cycling in terrestrial ecosystems at northern latitudes. Do increasing temperatures cause a stress response reflected in expression levels of selected stress-response genes and do stress response patterns differ between coastal and inland habitats? As mutualistic symbioses, lichens offer the possibility of analyzing molecular stress responses in a particularly tight interspecific relationship. Using real-time PCR quantification of 38 transcripts, differential expression was demonstrated for nine cyanobacterial and nine fungal stress response genes (plus the fungal symbiosis related lec2 gene) at 15°C and 25°C vs. 5°C indicating temperature stress for both symbionts. Principle component analysis (PCA) revealed two gene groups differing in temperature response patterns. Whereas a set of cyanobacterial DNA repair genes and the fungal lec2 (PC1 group) showed a strongly correlated expression drop at 15°C vs. 5°C, most fungal candidates (PC2 group) showed increased expression at 25°C vs. 5°C. Furthermore, PC1 genes differed more strongly in temperature response along an elevation gradient than between habitat categories. The correlated downregulation of lec2 and cyanobacterial DNA repair genes suggests a possible interplay between the symbionts warranting further studies.