Cross-talk of Calcium- and Energy Signalling in Plants

In order to survive in their natural habitats, plants need to be able to react and to acclimate to changing environmental conditions and to defend themselves against stresses such as drought, heat, or pathogen attack. To this end, plants acquired sophisticated signalling and defense mechanisms enabling them not only to defend themselves, but also to regulate the allocation of their resources in order to balance growth and stress defense. This ability is essential for their growth performance, which is, in the case of crop plants, the key determinant for yield. Particularly in view of the global climate change and an ever increasing world population, this aspect becomes more and more important. Increasing periods of drought stress and flooding in combination with pest and pathogen attack has led to significant crop losses during the past years. Accordingly, yield stability under detrimental growth conditions has become an important research focus in agriculture and target for plant breeding. To understand the regulation and coordination of these processes is of fundamental importance for future applied research in this direction. This is the main focus of this project. We will analyse two principal signalling pathways in plants, which are also highly conserved during evolution: Calcium-dependent and protein kinase-dependent signalling. Both mechanisms are active under similar conditions, and - at least partially they have also the same targets for regulation. Therefore the question emerges why that is the case, is there really overlap or rather a complementarity? A second aspect of this work is the question for the subcellular localization: Where in the cell are these proteins active and could a spatial separation of these proteins maybe explain their apparent redundancy? We will make use of a number of genetic and biochemical tools we have generated over the last years to answer these questions. Interaktionen zwischen Calcium- und energieabhängigen Signalwegen in Pflanzen PR Zusammenfassung Um in ihrer natürlichen Umgebung zu überleben, müssen Pflanzen in der Lage sein, sich an wechselnde Umweltbedingungen anzupassen und sich gegen Stress wie z.B. Trockenheit, Hitze oder Pathogen-Befall zu wehren. Dafür haben Pflanzen ausgeklügelte Verteidigungsstrategien entwickelt. Diese erlauben es ihnen nicht nur sich gegen diese Widrigkeiten zu wehren, sondern auch ihre Ressourcen effizient einzusetzen und damit Wachstum und Verteidigung in einen gesunden Einklang zu bringen. Diese Fähigkeit ist somit für ein optimales Wachstum und somit - im Falle von Kulturpflanzen - einen maximalen Ernteertrag entscheidend. Gerade im Hinblick auf den Klimawandel und die ständig steigende Weltbevölkerung

Due to their sessile life style, plants need to acclimate to changing environmental conditions continuously in order to survive. The environmental changes might be fluctuations in the available light energy caused by clouds or other stress conditions such as drought-, heat- or pathogen stress. As fast reaction to such changes plants, like all other living organisms, employ mechanisms of signal transduction in order to acclimate and survive in the new environmental condition. Plants have a huge repertoire of components involved in signal transduction and often different pathways are being used which lead in the end to the same response. One key issue for acclimation is the management of energy in order to channel the available resources into stress response and defence processes. This energy management is performed by a group of evolutionarily highly conserved molecular switches, so-called protein kinases. These include the cAMP kinases in animals and the SnRK kinases in plants, respectively. In parallel, also calcium signals are part of these regulatory processes. In this project we studied how different kinases share their job of transmitting an environmental signal, where they act synergistically and finally how important is their localization in different compartments of the cell to reach different targets. We found that the cAMP/SnRK kinases act mainly in the cytosol and are being regulated not only by the available energy but also by the redox potential of the cell. The most important targets of these kinases are the metabolic activity of different enzymes and the regulation of gene expression in response to stress conditions. These will then affect also processes at other compartments of the cell such as mitochondria or chloroplasts. Calcium signals in contrast, regulate a different group of kinases and act often in close proximity to membranes, e.g. by regulating membrane proteins such as ion channels. However, also this group of Calcium-dependent kinases regulates cellular metabolism as well. This is also done by the regulation of gene expression, but uses other components as compared to the cAMP/SnRK kinases. Interestingly, we observed that the subcellular localization is of crucial importance for the function of the Calcium-dependent kinases. If these kinases are, for example, localized exclusively at the plasma membrane und not in the nucleus - the place of gene expression - the plants cannot grow normally and die eventually. A similar effect has not been observed for the cAMP/SnRK kinases. This shows clearly that the correct subcellular localization is crucial for the function of the kinase and furthermore indicates that these pathways regulate different targets, resulting in a similar acclimation in the end.