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Evolving Phenolic Roles in Host Defense: The Cases of ‘Candidatus Liberibacter solanacearum’ Potato Infections and that of Grapevine Pathogens
Christopher Wallis: USDA ARS; Steven Lee: USDA ARS; Elizabeth Rogers: USDA ARS FDWSRU; Erin Galarneau: University of California Davis; Kendra Baumgartner: USDA ARS
<div>Upon infection, plants produce phenolic compounds presumably to defend against pathogens and assist in tissue repair. However, phenolic production in response to infection by ‘<i>Candidatus </i>Liberibacter solanacearum’ (Lso), causal agent of zebra chip disease, was linked directly to increased browning symptoms in freshly-sliced potato tubers. Furthermore, potato breeding lines deemed “tolerant” of Lso infections, due to lack of browning symptom development, accumulated lower phenolic levels following infection compared to susceptible varieties, suggesting the mechanism of tolerance was a lack of large-scale induced phenolic production as a host response. Likewise, there is building evidence that <i>Xylella fastidiosa</i>, causal agent of Pierce’s disease of grapevine,<i> </i>also might benefit from host phenolic production, as in culture this bacteria appears to consume certain phenolic compounds and grows better when phenolics are present at physiological levels. Finally, recent experiments observed that grapevine fungal pathogens deemed aggressive were able to consume or otherwise eliminate certain phenolics from media whereas less aggressive pathogens could not. In sum, phenolics have more complicated roles in plant-pathogen interactions than previously thought and, in some cases, phenolics may benefit pathogens more than plant hosts. <p> </div>

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