Global warming with its increased frequency of severe weather scenarios is a tremendous challenge for photosynthetically active organism and their communities. For example, increased water temperatures of lakes lead to severe threats of phytoplankton communities and a remarkable loss of biodiversity. The increased occurrence of toxic algal blooms is just one alarming extreme that shows how our major basis for drinking water, food, and recreation is jeopardized by global warming. Despite this relevance, little is known about how warming affect the molecular physiology of individual algal species and how phytoplankton achieves temperature acclimation as community. A comprehensive knowledge about such cellular processes is essential for water quality models and future endeavors to counteract ecosystem collapses.
In addition, the summer of 2018 drastically showed how Middle Europe will be challenged by more severe heat and drought waves which will cause substantial annual crop losses. Thus, the targeted design of stress-tolerant crop plants is a major and unavoidable task of modern plant biology in order to face the food demand of an increasing world population
These ambitious goals demand for a deep understanding of molecular mechanisms underlying acclimation and the stress response in phytoplankton species and higher plants. Temperature acclimation involves severe reorganization on multiple cellular levels including adapted gene expression and protein synthesis, as well as altered activities of enzyme and whole pathways that leads to changed primary and secondary products.
For a better understanding of these processes, it is essential to reveal and characterize central players that act as modulators and regulators during acclimation of plant cells.
Protein synthesis in the context of acclimation
Protein synthesis and subsequent folding of nascent polypeptides is one of the central processes governing the reorganization of a cellular proteome during acclimation. Previously, ribosomes - the synthesis machineries translating the genomic information into polypeptides – were considered as rather passive units. However, it is now understood that ribosomes are actually finely-tuned hubs, that are central in sensing and regulating protein homeostasis. Consequently, aim of our research is to better understand the regulation of protein synthesis and folding during acclimation of plant cells. We are especially interested in understanding these processes in chloroplasts of eukaryotic organism, since these organelles have an additional challenge during protein biogenesis. Besides the import of nucleus-encoded proteins, chloroplasts possess their own little genome and ribosomes. This means that proteins from two origins need to be orchestrated in order to achieve a balanced proteome, a process which is again highly responsive to environmental input.
Throughout their lifespan, proteins are guided by a number of factors that facilitate their maturation and that help proteins to maintain their functionality even under stress and denaturing conditions. Many of these factors belong to the family of molecular chaperones. Cells harbor structurally and functionally distinct classes of chaperones that vary in size and complexity. The diversity ranges from chaperones that only bind to misfolded polypeptides to prevent their aggregation to those that recognize specific substrate proteins and facilitate their folding to the native state. Further, chaperones are involved in the translocation of partially unfolded proteins across membranes, complex assembly and disassembly, and many other regulatory processes within the cell.
Our methodological portfolio comprises systems-biological and quantitative approaches such as ribosome profiling, transcript analysis and proteomics as well as protein-biochemistry and molecular tools for the investigation of individual components.
Chlamydomonas reinhardtii as model organism
Currently, a major part of our research is conducted with the well-established unicellular model alga Chlamydomonas reinhardtii,since work with a uniformly growing cell culture has several advantages for the global analysis of processes such as cellular reprogramming on the level of protein synthesis. However, an important aim of our current research is the identification of either evolutionary conserved processes or fundamental differences between single-celled aquatic organisms and more complex land plants, allowing to transfer knowledge from model organism to other ecological or agricultural relevant species. Consequently, all our current projects involve interspecies comparisons both on the level of global processes (such as protein synthesis) or functional studies involving individual factors (e.g. the chloroplast chaperone Trigger Factor).