Plant Disease Resistance and Pathogen Virulence

Just like any living organism plants can fall victim to microbial pathogens and had to evolve defense strategies for survival. The immune system of plants is remarkable similar to innate immunity of animals. A number of immune receptors recognize diverse pathogen derived molecules and as a result trigger a multitude of immune reactions including the production of antimicrobial compounds. The efficacy of the plant immune system forced pathogens to evolve counter strategies in form of effectors that are delivered into the host with the aim to sabotage plant immune responses and, thus, act as virulence factors. My group is mainly interested in the interaction of plants with the oomycete pathogen genus Phytophthora that includes many notorious pathogens of important crop plants.

Our current interest are:

• 1. What plant immune reactions are important for defense against pathogens?
  1. We are especially interested to identify proteins with antimicrobial activities and determine their mode of action. As an example, we have recently identified the long-sought biochemical function of the antimicrobial protein PATHOGENESIS-RELATED 1 (PR-1). PR-1 is a sterol-binding protein that sequester sterols from microbial membranes. As a sterol-auxotroph organism Phytophthora is especially sensitive to PR-1. In a collaboration with ETH Zürich we became also interested in nematicidal proteins as nematodes are an underestimated threat to agricultural production. This research may contribute to improvement of disease resistance of crop plants.
• 2. How do pathogens undermine plant disease resistance?

  We aim to determine the molecular targets of pathogen effector proteins (virulence factors) in order to learn what pathogens consider important processes worthwhile to be manipulated. By changing the sequence of target proteins or applying a decoy strategy it may be possible to evade the effect of the most powerful pathogen effectors and, thus, decrease pathogen virulence.

• 3. Pathogen effectors as molecular tools for cell biology.

  Host targets of pathogen effector are not limited to proteins with a direct role in plant disease resistance. Among our identified host targets are proteins that play roles in the secretory process or in the control of plasmodesmata aperture. One of the effectors targets e.g. many members of the subfamily A of RAB GTPases that regulate vesicular trafficking. We have shown that the effector inhibits the secretion of antimicrobial compounds. Using this effector as molecular tool can help to differentiate between RABA-dependent and RABA-independent secretory processes. This is difficult to achieve otherwise as the RABA GTPase family includes 24 members. Effectors targeting plasmodesmata are promising tools to study cell to cell communication.

• 4. Actinomycetes with biocontrol potential.

  There is an urgent need for sustainable protection of crop plants. One strategy is to use beneficial biocontrol microorganisms to fight pathogens. Actinomycetes are a great source of antimicrobial compounds including many commercial antibiotics. We recently started to screen Actinobacteria isolated from the field for their potential to protect plants from disease. Our major goal is to identify antimicrobial compounds and their mode of action.