The role of bacterial extracellular RNAs in plant infections with Xylella

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The infection success of pathogens depends on the delivery of virulence factors, so-called effectors, into host cells to circumvent plant immunity. Since 2013, Xylella fastidiosa (Xf) emerged as a bacterial pathogen in Europe associated with devastating epidemics in olive, almond and citrus trees. Lacking a Type III system and its secreted effectors, the mechanism used by Xf to suppress host immunity remain unanswered. Extracellular vesicles (EVs) are important bacterial structures, which have been associated with Xf virulence. This subproject will evaluate the role of EVs from Xf in host infection. We recently established Xf infection in Arabidopsis and observed both immunogenic and immune-suppressive activities of Xf EVs. Detection of RNA-binding proteins and RNAs at EVs suggests that EVs could transport bacterial extracellular RNA (exRNA) species. Our goal is to identify the EV RNA repertoire associated with Xf disease and to address the modulation of the plant’s immune system by EV RNAs. To address whether signatures of EV RNA species and host targets are common across microbial species, we will contribute to comparative studies within the RU5116. Benefitting from RU5116 research, we will explore RNA-mediated silencing against Xf. Together, this subproject will lead to new insights into the mechanisms contributing to pathogen virulence, in particular for Xf, and ultimately aims to identify novel pathogen effectors and host targets that, when targeted, will result in pathogen non-virulence and plant resistance.