ERC FUNDED PROJECTS

Mechanisms governing interaction between multicellular organisms and microbes are central for understanding pathogenesis, symbiosis and the function of ecosystems. We propose to address these mechanisms by pioneering an interdisciplinary approach for understanding cellular signalling, response processes and organ development. The challenge is to determine factors synchronising three processes, organogenesis, infection thread formation and bacterial infection, running in parallel to build a root nodule hosting symbiotic bacteria. We aim to exploit the unique possibilities for analysing endocytosis of bacteria in model legumes and to develop genomic, genetic and biological chemistry tools to break new ground in our understanding of carbohydrates in plant development and plant-microbe interaction. Surface exposed rhizobial polysaccharides play a crucial but poorly understood role in infection thread formation and rhizobial invasion resulting in endocytosis. We will undertake an integrated functional characterisation of receptor-ligand mechanisms mediating recognition of secreted polysaccharides and subsequent signal amplification. So far progress in this field has been limited by the complex nature of carbohydrate polymers, lack of a suitable experimental model system where both partners in an interaction could be manipulated and lack of corresponding methods for carbohydrate synthesis, analysis and interaction studies. In this context our legume model system and the discovery that the legume Nod-factor receptors recognise bacterial lipochitin-oligosaccharide signals at their LysM domains provides a new opportunity. Combined with advanced bioorganic chemistry and nanobioscience approaches this proposal will engage the above mentioned limitations.

2 399 127 €

Start date: 2011-05-01, End date: 2016-04-30

During an organism’s development it must integrate internal and external information. An example in plants, whose development stretches across their lifetime, is the coordination between environmental stimuli and endogenous cues on regulating the key hormone gibberellin (GA). The present challenge is to understand how these diverse signals influence GA levels and how GA signalling leads to diverse GA responses. This challenge is deepened by a fundamental problem in hormone research: the specific responses directed by a given hormone often depend on the cell-type, timing, and amount of hormone accumulation, but hormone concentrations are most often assessed at the organism or tissue level. Our approach, based on a novel optogenetic biosensor, GA Perception Sensor 1 (GPS1), brings the goal of high-resolution quantification of GA in vivo within reach. In plants expressing GPS1, we observe gradients of GA in elongating root and shoot tissues. We now aim to understand how a series of independently tunable enzymatic and transport activities combine to articulate the GA gradients that we observe. We further aim to discover the mechanisms by which endogenous and environmental signals regulate these GA enzymes and transporters. Finally, we aim to understand how one of these signals, light, regulates GA patterns to influence dynamic cell growth and organ behavior. Our overarching goal is a systems level understanding of the signal integration upstream and growth programming downstream of GA. The groundbreaking aspect of this proposal is our focus at the cellular level, and we are uniquely positioned to carry out our multidisciplinary aims involving biosensor engineering, innovative imaging, and multiscale modelling. We anticipate that the discoveries stemming from this project will provide the detailed understanding necessary to make strategic interventions into GA dynamic patterning in crop plants for specific improvements in growth, development, and environmental responses.

1 499 616 €

Start date: 2018-01-01, End date: 2022-12-31

Cell fusion is critical for fertilization and development, for instance underlying muscle or bone formation. Cell fusion may also play important roles in regeneration and cancer. A conceptual understanding is emerging that cell fusion requires cell-cell communication, polarization of the cells towards each other, and assembly of a fusion machinery, in which an actin-based structure promotes membrane juxtaposition and fusogenic factors drive membrane fusion. However, in no single system have the molecular nature of all these parts been described, and thus the molecular basis of cell fusion remains poorly understood. This proposal aims to depict the complete fusion process in a single organism, using the simple yeast model Schizosaccharomyces pombe, which has a long track record of discoveries in fundamental cellular processes. These haploid cells, which fuse to generate a diploid zygote, use highly conserved mechanisms of cell-cell communication (through pheromones and GPCR signaling), cell polarization (centred around the small GTPase Cdc42) and fusion. Indeed, we recently showed that these cells assemble an actin-based fusion structure, dubbed the actin fusion focus. Our five aims probe the molecular nature of, and the links between, signaling, polarization and the fusion machinery from initiation to termination of the process. These are: 1: To define the roles and feedback regulation of Cdc42 during cell fusion 2: To understand the molecular mechanisms of actin fusion focus formation 3: To identify the fusogen(s) promoting membrane fusion 4: To probe the GPCR signal for fusion initiation 5: To define the mechanism of fusion termination By combining genetic, optogenetic, biochemical, live-imaging, synthetic and modeling approaches, this project will bring a molecular and conceptual understanding of cell fusion. This work will have far-ranging relevance for cell polarization, cytoskeletal organization, cell signalling and communication, and cell fate regulation.

1 999 956 €

Start date: 2016-10-01, End date: 2021-09-30

Plants differ strikingly from animals by the almost total absence of cell migration in their development. Plants build their bodies using a hydrostatic skeleton that consists of pressurized cells encased by a cell wall. Consequently, plant cells cannot migrate and must sculpture their bodies by orientation of cell division and precise regulation of cell growth. Cell growth depends on the balance between internal cell pressure – turgor, and strength of the cell wall. Cell growth is under a strict developmental control, which is exemplified in the Arabidopsis thaliana root tip, where massive cell elongation occurs in a defined spatio-temporal developmental window. Despite the immobility of their cells, plant organs move to optimize light and nutrient acquisition and to orient their bodies along the gravity vector. These movements depend on differential regulation of cell elongation across the organ, and on response to the phytohormone auxin. Even though the control of cell growth is in the epicenter of plant development, protein networks steering the developmental growth onset, coordination and termination remain elusive. Similarly, although auxin is the central regulator of growth, the molecular mechanism of its effect on root growth is unknown. In this project, I will establish a unique microscopy setup for high spatio-temporal resolution live-cell imaging equipped with a microfluidic lab-on-chip platform optimized for growing roots, to enable analysis and manipulation of root growth physiology. I will use developmental gradients in the root to discover genes that steer cellular growth, by correlating transcriptome profiles of individual cell types with the cell size. In parallel, I will exploit the auxin effect on root to unravel molecular mechanisms that control cell elongation. Finally, I am going to combine the live-cell imaging methodology with the gene discovery approaches to chart a dynamic spatio-temporal physiological map of a growing Arabidopsis root.

1 498 750 €

Start date: 2019-01-01, End date: 2023-12-31