Research projects

Plants are facing constant environmental changes and therefore have to readily respond and adapt to the environment for optimal growth and reproduction. This requires the coordination of cell division and differentiation according to the developmental stages through their entire life cycle, which in turn requires the strict regulation of protein synthesis, intracellular transport of proteins, endocytosis and protein degradation. 

Plasma membrane receptors play a crucial role in the coordination of extracellular signals and intracellular responses that enable plants to react to environmental changes and stress. Regulation of the abundance of plasma membrane receptors by endocytosis-dependent protein degradation in the vacuole is an important regulatory mechanism in a variety of signaling pathways such as phytohormone signaling and biotic- and abiotic stress responses.

Our group is interested in the elucidation of the molecular mechanisms that regulate ubiquitin-dependent protein degradation. Our current projects are as follows.

1. Regulation of ubiquitination in intracellular membrane trafficking of plants

Ubiquitination is a post-translational process in which ubiquitin - a highly conserved small protein of 76 aa - is covalently attached to substrate proteins and is, among others, a signal for selective protein degradation. Depending on the modification type (mono-ubiquitination, K48, K63 and other linkages), ubiquitination can serve as signals in various cellular processes. Since many of these target proteins are key regulatory factors of different signaling pathways, it is essential that the processes of ubiquitin conjugation and deconjugation are strictly regulated.

We are interested in the molecular mechanisms by which ubiquitin is regulating these processes in the model plant Arabidopsis thaliana with a special focus on endocytosis and the subsequent protein transport to the vacuole. Using molecular biological, biochemical and cell biological methods, we are addressing the question as to how ubiquitination and deubiquitination are controlling plant growth and development at the molecular and cellular level.

2. Function of deubiquitinating enzymes in plants

The conjugation of ubiquitin molecules to its target proteins is a process that is mediated by the activity of E1, E2 and E3 enzymes, in which the combination of the E2 and E3 enzymes usually defines the ubiquitin chain-type to be conjugated as well as substrate specificity. Deubiquitination, on the other hand, is mostly carried out by a single DUB. Though the ubiquitination machinery plays a key role in determining target protein stability, DUBs can also influence target protein fate by removing the ubiquitin signals from the protein. In most of the cases the interaction of the DUB with the conjugated ubiquitin chain, rather than with the target protein itself, is sufficient for target deubiquitination. The spatio-temporal regulation of DUBs is therefore crucial for deubiquitination of the correct target proteins. Our aim is to characterize Arabidopsis DUBs that are involved in the regulation of protein stability and to understand their physiological functions.

3. Regulation of plant vacuole biogenesis

Throughout the lifecycle of a plant, vacuoles serve as storage compartments for various proteins and secondary metabolites and are also organelles in which toxic compounds are sequestered. Deciphering the molecular process underlying vacuole biogenesis, maintenance and vacuolar transport is important for our understanding of the function of this central organelle in cellular homeostasis. The molecular mechanisms of plant vacuole biogenesis are still poorly understood and therefore we aim to improve our understanding by identifying novel factors involved in vacuole biogenesis by screening and analyzing vacuole fusion defective (vfd) mutants. By means of map-based cloning and whole genome sequencing, we identified VFD1 as FYVE1. FYVE1 encodes for an endosome-localized Fab 1, YOTB, Vac 1, and EEA1 (FYVE) domain containing protein. We characterized the molecular function of FYVE1 also identified other proteins that are involved in vacuole biogenesis.