Functional characterization of bacterial type III effectors in plant cells

• Applicant: Professor Dr. Frederik Börnke
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems ; Plant Biochemistry and Biophysics
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 250452489

Pathogenicity of many Gram-negative pathogenic bacteria depends on a type III secretion system, which translocates bacterial effector proteins into the host cell. These type III effector proteins (T3Es) have evolved to function in a eukaryotic context in order to promote colonization of the host. The molecular mechanisms by which these T3Es alter host cellular processes are far from being understood. In our preliminary work we were able to show that HopZ1a, a T3E from Pseudomonas syringae, interacts with a previously uncharacterized remorin protein inside plant cells. Further interaction studies indicate that the remorin protein binds to and is specifically phosphorylated by the immune kinase PBS1 and also interacts with the E3 ligase SINA4. Overexpression of the remorin leads to increased basal PTI marker gene expression and induced ROS production after a flg22 stimulus. Our findings led to the hypothesis that the remorin might act in a complex together with PBS1 during PTI and hence is targeted by HopZ1a to manipulate immune signaling. Within the proposed project we will investigate the biochemical and molecular mechanism by which HopZ1a interferes with remorin function and how this leads to suppression of immunity. In addition, we could show that the T3E XopS form Xanthomonas campestris interacts inside the plant cell nucleus with a protein pair consisting of the transcription factor WRKY40 and an E3-ubiquitin ligase. The E3 ligase interacts with WRKY40 in vitro and in planta and ubiquitinates the transcription factor in vitro. Accordingly, transient expression in leaves of Nicotiana benthamiana suggests that WRKY40 undergoes rapid proteasomal protein turnover. However, WRKY40 protein strongly accumulates upon co-expression with XopS, indicating that XopS interferes with proteasomal turnover of WRKY40 and thus could interfere with defense gene induction that requires degradation of this negative regulator of plant defense. The second aim of the project is to unravel how XopS alters WRKY40 function and how this impacts on induced defense responses in host plants.

• DFG Programme: Research Grants