Many proteins are modified after their synthesis. We are interested in how the small modifier proteins ubiquitin and SUMO are linked to substrate proteins in plants, and how these processes change substrate properties. Covalent attachment of ubiquitin to substrate proteins is essential for many processes. Best known is its role in protein degradation. Several ubiquitin moieties, linked as a chain to the substrate protein, can serve as a signal for rapid proteolytic destruction of the substrate. An example for this function is the N-end rule pathway, which uses the amino-terminal residue of a protein to select substrates for degradation and is important for a plants response to anoxia, for germination and for senescence. However, ubiquitylation also has non-proteolytic functions. One ubiquitylation complex of interest to us operates at the cell membrane. The ubiquitin chains formed by this complex have a predominantly regulatory role, and seem to influence the activity state of certain membrane proteins. This process is important for correct establishment of the plant architecture.

Our second focus is a synthetic biology project, dealing with a so-called retrotransposon. Retrotransposons are pieces of DNA that can replicate more often than the normal genomic DNA. They do so by reverse transcribing their mRNA, and by inserting the ensuing DNA copy into the host genome, often at a random position. We want to convert retrotransposon Tto1 into a novel tool for plant investigation and improvement. On the way to this goal, we are learning a lot about the life cycle of this retrotransposon. Transposition of retrotransposons is usually induced by stress, and therefore not easy to control. We have modified Tto1 such that its transpositional activity can be induced by the chemical substances Estradiol or Dexamethasone. This novel regulatory circuitry is first tested in the model plant Arabidopsis thaliana and shall then be used in other plants including crops, which currently offer only limited options for genetic manipulation. For instance, insertion of Tto1 into a crop plant´s  genome may generate mutations for gene analysis, and genetic variability for breeding programs.