Department of Organismic Interactions

Research in the department of Organismic Interactions is focused on the mechanisms that enable biotrophic fungi to colonize plants and to cause disease. Biotrophic fungi establish interactions with plants in which the host tissue needs to be kept alive to sustain fungal growth. Initially, biotrophic fungi - like all microbes in contact with plants - are recognized by the plant immune system via conserved microbe-associated molecular patterns (MAMPS). Recognition involves Pattern Recognition Receptors and leads to the induction of plant defense responses in the course of which reactive oxygen species and antimicrobial compound detrimental to the pathogen are produced. This process is termed Pattern-Triggered Immunity (PTI). Successful pathogens need to downregulate PTI, and this is achieved through several hundred secreted effector molecules. Effectors can suppress PTI (effector triggered susceptibility, ETS) by downregulating respective plant genes, they can inhibit the enzymatic activity of plant enzymes attacking the pathogen, they can shield fungal hyphae from enzymatic attack and they can reprogram the metabolism of the host to meet pathogen needs.

In the department of Organismic Interactions we study the molecular function of secreted effectors of the corn smut fungus Ustilago maydis. This fungus produces more than 200 completely novel effector candidates whose expression occurs in discrete waves during plant colonization. U. maydis serves as a model for the large group of basidiomycete plant pathogens which include beside smut fungi also the obligate biotrophic rust fungi, some of the most devastating plant pathogens known.

We aim to answer the following questions:

  • How can we identify effectors which have a strong contribution to virulence?
  • Which plant proteins are interacting with virulence-promoting effectors and how is their activity changed by the effector?
  • How are fungal effector molecules taken up by host cells?
  • How is effector gene exression regulated and fine-tuned with fungal development during host colonization?

National and international collaborations:

• with G. Bange (SYNMIKRO, Marburg, Germany) with respect to structure determination of U. maydis effectors.
• with H. Link (SYNMIKRO, Marburg) with respect to cAMP measurements.
• with S. Rensing (Philipps-Universität Marburg, Germany) with respect to the bioinformatic analysis of RNAseq data and phylogenetic analyses.
• with T. Glatter (MPIterMIC) with respect to mass spectroscopy.
• with K. Snetselaar (St. Joseph's University, Philadelphia, USA) with respect to effector localization by EM.
• with R. Roth and U. Paszkowski (Cambridge University, UK) with respect to EM-analyses of biotrophic U. maydis hyphae after cryofixation.

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