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Oral: 16th I.E., Melhus


O antigen functions as a shield during the Xylella fastidiosa-grapevine interaction
J. RAPICAVOLI (1) (1) University of California, U.S.A.

Plant host recognition of conserved pathogen-associated molecular patterns (PAMPs) leads to activation of the first tier of the innate immune response, known as PAMP-triggered immunity (PTI). Successful plant pathogens must evade or overcome PTI to establish and cause disease. Suppression of PTI by secreted effector proteins is a well-known strategy employed by many bacterial plant pathogens. Xylella fastidiosa is a xylem-limited bacterium that causes destructive diseases such as Pierce’s disease (PD) of grapevine. X. fastidiosa lacks the quintessential Type III secretion system and its suite of effectors that could dampen PTI responses. Thus, the mechanisms utilized by this pathogen to combat PTI have remained obscure. Some bacterial pathogens can evade host recognition by actively altering the composition and/or structure of carbohydrates on the cell surface. We demonstrate that X. fastidiosa utilizes the prominent O antigen surface carbohydrate to shield PAMPs from early detection by the grapevine innate immune system, thus altering subsequent deployment of defense responses. We identified specific transcriptional and phenotypic responses activated by O antigen mutant strains during the early stages of infection in grapevine. These results provide unprecedented insight into the molecular mechanisms underlying this host-pathogen interaction.