Towards Identifying PAMPs from the Downy Mildew Pathogen Hyaloperonospora Arabidopsidis

Downy mildews are oomycete microbes and obligate parasites, belonging to the Order Peronosporales. They display a variety of hosts, infecting crop plants belonging to different families, such as lettuce, grapevine or tomato, but also ornamental plants. They develop in humid and moist conditions and represent a threat for growers and producers. The system composed by the plant Arabidopsis thaliana and its natural oomycete pathogen Hyaloperonospora arabidopsidis (Hpa) has been used as a model to investigate plant–oomycete pathogen interactions. We aimed to discover conserved molecules deriving from the pathogen, called PAMPs (pathogen-associated molecular patterns), which are recognized by the plant immune system and that are able to trigger an immune reaction in the plant. To look for PAMPs originating from Hpa, an extract from the spores of the pathogen has been obtained. The extract has been tested using an assay able to highlight one of the first signs of PAMP-triggered immunity (PTI): ROS production. Furthermore, it has been treated with proteinase K to better understand the nature of the active molecules. In addition, various mutants of putative receptors have been tested using the same assay. We demonstrated that the extract contains molecules able to trigger an immune reaction in Arabidopsis Col-0 plants and that the proteinase K-treated spore extract lost its immune triggering ability, indicating a proteinaceous nature of the active molecules. Testing the extract on mutant plants showed that the perception of the active molecules might be Bak1-dependent. Recent findings will be presented.