Kalina T HAAS Chargée de recherche

Paroi Primaire

ERC Starting Grant. In this project, we want to understand the core subcellular mechanism behind growth and shape formation in plants. Much research was largely focused on the indirect or long-term regulation of growth (e.g. through the control of gene expression). The identity of the rapid molecular mechanisms directly involved in growth, i.e. "The motor of growth", remains a mystery that we hope to unravel in this project. To do so,  we will use super-resolution, and optogenetics combined with multiplexed biochemical imaging to study subcellular regulation of growth orientation and the temporal dynamics of a putative growth motor. The results will be combined and integrated into a  quantitative and predictive model of growth recurrently tested and improved based on the data.

We will work on two main growth models in Arabidopsis thaliana  (1) the dark-grown hypocotyl to study highly anisotropic diffuse tissue growth and; (2) root hairs to study single-cell polarised tip growth. In root hairs, growth is happening in cycles and is correlated with the changes in biochemical and biophysical variables, such as the cell wall pH. These cyclic phenomena can be a direct manifestation of a growth motor. We will investigate whether cell expansion is inherently cyclic also on the tissue level using the dark-grown hypocotyl. We aim at establishing causal relations and temporal patterns of the putative elements constituting the motor of growth: pectin demethylation, pH, CrRLKL1 receptors, RALF (Rapid ALkalinization Factor) peptides, and factors involved in turgor-driven wall remodeling. To achieve this we will develop tools for optogenetics to rapidly perturb the system and multiplexed FRET biosensing to monitor effects in real-time. By simultaneously observing a combination of key variables, we will establish causal relations and order of events in a single growth cycle.

Our recent discovery of pectin nanofilaments showed that the organization of cell wall polymers controls growth anisotropy. Using super-resolution microscopy we will be studying how the cell wall organization is regulated by the cytoskeleton, cellulose deposition, and local stress distribution. Finally, we will work with different tissues and species to investigate the universality of the pectin-swelling-driven expansion model.