PLENARY ABSTRACT O–PL–001 Photosynthesis in the soil – past and present F. Garcia-Pichel1 1Arizona State University, Center for Fundamental and Applied Microbiomics, Tempe, AZ, United States Biological soil crusts (biocrusts) are microbial and/or cryptogamic photosynthetic communities that develop in areas where plant cover is restricted by aridity or other extreme conditions. During the last few decades we have learned much about the biology and ecological roles of biocrusts and true global extent of these communities, which I will briefly review. Evidence is now mounting that analogs of current cyanobacterial biocrusts were present extensively on land well before the advent of land plants, and that biocrusts may have been the main terrestrial ecosystem for much of the planet’s history. ORAL ABSTRACT • SYNTHETIC BIOLOGY O–A–001 Fixing CO2-fixation – redesigning photosynthesis with synthetic biology J. Zarzycki1 1Max Planck Institute for Terrestrial Microbiology, Department of Biochemistry and Synthetic Metabolism, Marburg, Germany RubisCO is considered a limiting factor in photosynthesis due to its low catalytic rate and promiscuity with oxygen, resulting in photorespiration. We hope to overcome the limitations of RubisCO based carbon fixation. Therefore, our lab is focusing on the discovery, characterization, and engineering of new CO2 fixing enzymes as well as their integration within synthetic and natural pathways. One example of such approaches is the creation of completely novel synthetic CO2 fixation cycles that are centered on carboxylases that are more efficient than RubisCO, as showcased by our so-called CETCH cycle. A second example is the engineering of new-to-nature carboxylases by making use of theoretically feasible reactions and develop new reactivities on the scaffold of existing enzymes. This enables us to extend the solution space for metabolic reactions and open new avenues for the realization of synthetic pathways, as illustrated by our Tartronyl-CoA module. The latter employs a non-natural engineered glycolyl-CoA carboxylase and harbors great potential as a more energy efficient and carbon-positive alternative route to photorespiration. 45 ORAL ABSTRACT • SYNTHETIC BIOLOGY O–A–002 FormatPlant – engineering CO2 neutral photorespiration in plants M. S. Roell1, A. Weber1 1Heinrich-Heine University, Institute of Plant Biochemistry, Düsseldorf, Germany The CO2-fixing enzyme Ribulose-1,5-bisphosphate-carboxylase/-oxygenase (Rubisco) is restricted by its slow turnover rate and its oxygenase activity. Resulting photorespiration reduces plant carbon efficiency and is a major target to improve plant growth and agricultural yield. Recent work demonstrated the benefits of chloroplastic photorespiratory bypasses on plant growth even 1 under field conditions . Maximizing plant carbon efficiency implies transforming photorespiration from a CO2 negative into a CO2 neutral process requiring bypassing the mitochondrial glycine decarboxylase (GDC), the major hub of photorespiratory CO2 loss. However, replacing the GDC requires an alternative provision of one carbon compounds due to its dual role in photorespiration and one carbon metabolism. In FormatPlants one carbon compounds are produced via cytosolic formate assimilation, based on tetrahydrofolate intermediates, making GDC compensable. Subsequent condensation of 5,10-methylen-tetrahydrofolate with photorespiratory derived glycine to make serine, transforms plant photorespiration into a CO2 neutral process. Initial labelling experiments with exogenously supplied 13C-labelled formate indicated that in Arabidopsis the capacity for formate assimilation is limited and metabolic flux is directed towards methionine production. Therefore, we implemented a cytosolic four-step synthetic pathway for the efficient assimilation of formate via tetrahydrofolate intermediates into serine. Low endogenous formate concentrations will prevent high pathway flux towards serine production. We identified mitochondrial Arabidopsis formate dehydrogenase (FDH) as second contributor to photorespiratory CO2 loss and knockout FDH using the CRISPR/Cas9 system. References [1] South, P. F., Cavanagh, A. P., Liu, H. W. & Ort, D. R. Synthetic glycolate metabolism pathways stimulate crop growth and productivity in the fiel. Science 363, (2019). O–A–003 Using a marine microalga as a chassis for biological degradation of plastics D. Moog1, J. Schmitt1, J. Senger2, J. Zarzycki2, K. H. Rexer3, U. Linne4, T. Erb2, U. G. Maier1 1Philipps University Marburg, Laboratory for Cell Biology, Marburg, Germany 2Max Planck Institute for Terrestrial Microbiology, Marburg, Germany 3Philipps University Marburg, Department for Mycology, Marburg, Germany 4Philipps University Marburg, Massenspektrometrie und Elementanalytik, Marburg, Germany Question: Plastic is an extremely useful material with a wide range of applications and seemingly no longer indispensable for our daily life. However, the tremendous amount of plastic waste produced year in and year out has become a major ecological issue on our planet in the last decades, mostly due to inadequate disposal and the high durability of the synthetic material. The consequences of plastic pollution for Earth's ecosystems are so far unforeseeable, but it becomes more and more evident that the plastic accumulating in nature is harmful for life. Although bioremediation would be highly desirable and probably a solution to the problem of continuous plastic pollution, the bulk of plastics produced so far is not biodegradable and thus extremely durable. The reason for this is the artificial nature of plastic and its relatively short existence on Earth. Remarkably, some life- forms have acquired the capability to degrade plastics and can use them as a nutrient for growth. Such organisms might provide promising solutions for bioremediation of plastic waste in future biotechnological applications. Methods: The diatom Phaeodactylum tricornutum is a photosynthetic marine microalga that has developed into an extremely valuable model system for molecular biology and biotechnology. In this project, we modified P. tricornutum via synthetic biology using bacterial genes, which encode plastic-hydrolyzing enzymes, to generate a chassis for the efficient production and secretion of their products. To test the plastic degradation ability of the enzymes secreted by the modified microalgae, we used several techniques including Western Blot, scanning electron microscopy and ultra high performance liquid chromatography. Results: Via these methods, we verified the successful generation of a photosynthetic microalga cell factory for biological degradation of plastics in a saltwater-based environment at mesophilic temperatures. Conclusions: Our results demonstrate the potential of the diatom for future applications in biological plastic degradation up to the generation of eco-friendly and comprehensive recycling processes for synthetic plastics. 46 ORAL ABSTRACT • EVOLUTION, DIVERSITY AND PHYLOGENY O–B–001 The early evolution of land plants as inferred by comparative genomics S. A. Rensing1 1University of Marburg, Faculty of Biology, Marburg, Germany The conquest of land by plant life was a singular event occurring ca. 500 Ma ago, in the Ordovician. Some lineages of charophyte freshwater algae share a common ancestry with the land plants (Embryophyta). Synapomorphies that already evolved in the water include land plant type cell wall synthesis and division, polyplastidy as well as some phytohormones and transcription factors. Extant representatives of the earliest splits that occurred after the establishment of land plants are the bryophytes (hornworts, mosses and liverworts). Although, like all land plants, they feature the alternation of a haploid and a diploid multicellular generation, the haploid gametophyte represents the dominant phase in bryophytes. By comparison with diploid-dominant flowering plants we unravel more and more gene regulatory networks and key transcription factors that control similar processes in dominant gametophytes and sporophytes. Evolution of land plant complexity thus is rooted in gene networks recruited from gametophytes. Whole genome duplications, and increase of transcriptional network complexity, are hallmarks of plant evolution. By using comparative genomics we are starting to comprehend how complexity evolution occurs. I will present examples mainly from the bryophytes and charophytes to illustrate how inference of ancestral states and complexity evolution of land plants is aided in particular by non-seed plant genomes. Keywords : Evolution, bryophyte, charophyte, complexity, transcriptional regulation O–B–002 Convergent molecular evolution of carnivorous plants K. Fukushima1 1University of Würzburg, Department of Botany I, Würzburg, Germany Although evolutionary processes are largely stochastic, natural selection can drive recurrent adaptations leading to convergence, the repeated emergence of similar features in distantly related organisms. Prevalence of phenotypic convergence is underpinned by various examples throughout the entire tree of life, such as camera eyes of vertebrates and cephalopods, wings of birds and bats, and trap leaves of distantly related carnivorous plants. Because the multiple emergence of such complex traits by neutral evolution alone is extremely unlikely, convergence has been considered strong evidence for natural selection. Carnivorous plants are a prominent example of convergence in 200 million years of flowering plant evolution.