Probing the contractile vacuole as Achilles’ heel of the biotrophic grapevine pathogen Plasmopara viticola
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The causative agent of Grapevine Downy Mildew, the oomycete Plasmopara viticola, poses a serious threat to viticulture. In the current work, the contractile vacuole of the zoospore is analysed as potential target for novel plant protection strategies. Using a combination of electron microscopy, spinning disc confocal microscopy, and video differential interference contrast microscopy, we have followed the genesis and dynamics of this vacuole required during the search for the stomata, when the non-walled zoospore is exposed to hypotonic conditions. This subcellular description was combined with a pharmacological study, where the functionality of the contractile vacuole was blocked by manipulation of actin, by Na, Cu, and Al ions or by inhibition of the NADPH oxidase. We further observe that RGD peptides (mimicking binding sites for integrins at the extracellular matrix) can inhibit the function of the contractile vacuole as well. Finally, we show that an extract from Chinese liquorice (Glycyrrhiza uralensis) proposed as biocontrol for Downy Mildews can efficiently induce zoospore burst and that this activity depends on the activity of NADPH oxidase. The effect of the extract can be phenocopied by its major compound, glycyrrhizin, suggesting a mode of action for this biologically safe alternative to copper products.
KeywordsContractile vacuole Downy Mildew Glycyrrhizin Plasmopara viticola RGD peptides
We gratefully acknowledge Joachim Daumann and Kerstin Huber (Botanical Garden of the Karlsruhe Institute of Technology) for efficient support with the plant material. Also, we acknowledge Prof. Dr. Otmar Spring and Dr. Javier Goméz (University of Hohenheim) for kindly providing single-sporangia strains of P. viticola. This work was supported by the VITIFUTUR Interreg V Upper Rhine project co-financed by the European Union/European Regional Development Fund (ERDF) and the German Federal Agency for Agriculture (Programme for Sustainable Agriculture, BÖLN).
Compliance with ethical standards
This study was supported by funds from the BACCHUS Interreg IV Upper Rhine project co-financed by the European Union/European Regional Development Fund (ERDF) and the German Federal Agency for Agriculture (Programme for Sustainable Agriculture, BÖLN).
Conflict of interest
The authors declare that they have no conflict of interest.
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