Group Christian Koch


Yeast Cell Biology

Research of the Fungal Cell Biology group is concerned with the analysis of gene regulation and cell division in the yeast Saccharomyces cerevisiae and with the analysis of phytopathogenic fungi. Using genetic and biochemical techniques, we study transcription factors involved in cell cycle regulation, stress response and gene silencing in yeast. Together with the lab of U. Sonnewald and L. Voll , we study models of compatible plant fungal interactions. Our studies concentrate on the analysis of changes in fungal physiology upon infection and are aimed at identifying fungal genes and effectors involved in the communication with the plant host.

Yeast Cell Biology

Regulated gene expression is not only a vital determinant of differentiation and development, but also important for coordinating events during the cell division cycle. In particular the decision to enter a new cell cycle in late G1-phase is largely determined by regulated transcription of many genes involved in S-phase control. To understand how expression of such genes is regulated, we are studying the regulation, structure and function of the cell cycle regulated transcription factors Swi4, Mbp1 and Swi6. Their timely activation in late G1 is particularly important to control cell size in yeast. Another aspect of our work concerns the identification of other regulators of cell size. We are studying this problem genetically by screening for mutants with altered cell size. In particular, we found the histone deacetylase complex Rpd3/Sin3 to be important for size control in daughter cells. It is becoming increasingly clear that many steps during RNA polymerase II dependent gene expression are coordinated by regulating the physical association of different multienzyme complexes with the polymerase itself. One of the PolII associated protein complexes is the Paf1-Ctr9 complex, which is associated with the elongating polymerase and helps to coordinate several events during the transcription cycle like, histone methylation and also gene silencing. We are studying components of the Paf1 complex and their interactions.

Fungal plant pathogens

In collaboration with the lab of  L. Voll , we are studying the interaction of the model plant Arabidopsis thaliana with the fungal pathogen Colletotrichum higginsianum. Since, both the host plant and the fungus are genetically tractable this pathosystem is well suited to study the molecular mechanisms of pathology. C. higginsianum belongs to the group of hemibiotrophic fungi which includes some of the economically important crop pathogens like Magnaporthe grisea. Currently, we are using insertional mutagenesis of Colletotrichum higginsianum by Agrobacterium mediated transformation (ATMT) to identify genes required for plant infection. We are particularly interested in the early stages of infection when the pathogen establishes a biotrophic relationship with its host. In another project, we use tagged fungal proteins to analyse the infection process on the cellular level.

Tagged nuclei and plasmamembrane of C. higginsianum

Appressoria of C. higginsianum on plant surface.