Understanding the decoding of calcium signals by calcium dependent enzymes and channels in plants - integrating experimental data and computational modeling

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Calcium signalling occurs in many different cell types in animals, plants, fungi and microorganisms and carries information from agonists bound to receptors at the cell membrane to targets in the interior of the cell. The information carried serves an amazing variety of different purposes. Thus, in plants, many intrinsic developmental processes, but also immediate responses to environmental factors are mediated by calcium. How this multitude of functionalities is conveyed by one and the same second messenger is still only partially understood. This is especially true in plant physiology. We would like to increase the understanding of the information processing by following two objectives.First of all, in collaboration with the groups of Kudla, Grill, Hedrich and Romeis, we would like to make use of the experimentally determined kinetics of calcium dependent enzymes and channels in A. thaliana to build up detailed kinetic models of these. These models are then coupled to actual experimental data of calcium transients measured by the partners in plant cells. Thus, without having a detailed mechanistic model of calcium signal transduction in plant cells, it will be possible to study the signal decoding of calcium transients by calcium dependent proteins in detail. Our second goal is to build up an actual computational model of calcium signalling in plant cells. Compared to existing work and based on our work within this project, this model should be biochemically mechanistic and quantitative to the most possible degree with the current knowledge, but should be also flexible enough to allow adjustment to tissue and organism specific conditions in subsequent project. We are aware that this is actually a challenge due to the fact that only few of the players of calcium signalling in plants have been characterized in detail and others might not even be known so far. However, even early studies on calcium signalling in vertebrates which also lacked a lot of molecular detail, have been beneficial for the progress of calcium research due to the ability to conduct virtual experiments and integrate current knowledge to probe certain hypothesis and to understand the qualitative, as well as quantitative nature of the system. Thus, important mechanisms have been discovered due to the inability of models to fit the actual data hinting to additional players. We expect that this will be also the case in this project. We will focus on calcium signalling in the context of ABA and salt (NaCl) responses in root as well as ABA responses in guard cells, since these are the systems which are studied in great detail within the research group and for which a unique collection of data will be available as a basis for our models.