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Identification of a novel target of the bacterial effector HopZ1a

Philip Albers: Leibniz-Institute of Vegetable and Ornamental Crops (IGZ)

<div>The plant pathogen <em>Pseudomonas syringae </em>is a gram-negative bacterium which infects a wide range of plant species including important crops plants. To suppress plant immunity and cause disease <em>P.syringae </em>injects type-III effector proteins (T3Es) into the plant cell cytosol. In this study, we identified a novel target of the well characterized bacterial T3E HopZ1a. HopZ1a is an acetyltransferase that was shown to disrupt vesicle transport during innate immunity by acetylating tubulin. Using a yeast-two-hybrid screen approach, we identified a REMORIN (REM) protein from tobacco as a novel HopZ1a target. HopZ1a interacts with REM at the plasma membrane (PM) as shown by split-YFP experiments. Interestingly, we found that PBS1, a well-known kinase involved in plant immunity also interacts with REM in pull-down assays<em>, </em>and at the PM as shown by BiFC. Furthermore, we confirmed that REM is phosphorylated by PBS1 <em>in vitro</em>. Overexpression of REM provokes the upregulation of defense genes and leads to disease-like phenotypes pointing to a role of REM in plant immune signaling. Further protein-protein interaction studies reveal novel REM binding partners with a possible role in plant immune signaling. Thus, REM might act as an assembly hub for an immune signaling complex targeted by HopZ1a. Taken together, this is the first report describing that a REM protein is targeted by a bacterial effector. How HopZ1a might mechanistically manipulate the plant immune system through interfering with REM function will be discussed.</div>