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The role that Xylella fastidisoa pnp plays in cold response and virulence
Xylella fastidiosa is a xylem-obligate plant pathogenic bacterium that causes disease in diverse crop plants. In grapevines, the infection is known as Pierce’s disease, which is limited to regions with warmer climates and fails to appear in cold climates. In previous research, it was observed that grapevines infected with X. fastidiosa can lose the infection during the winter season. However, this phenomenon (termed “cold curing”) is not completely understood. X. fastidiosa lacks certain aspects of bacterial cold response, including cold-inducible cold shock proteins. Due to the known role of cold shock proteins in RNA stabilization, this study investigated the role of RNA metabolism in X. fastidiosa in response to cold temperatures. Specifically, we characterized a purine nucleotide phosphorylase gene (pnp). We utilized knockout mutagenesis to evaluate the role of pnp in X. fastidiosa cold survival, in planta virulence, and cold-inducible gene expression. Our results suggest that X. fastidiosa pnp does not have reduced survival at 4℃ or in planta, but it is less virulent than the wild type, Stag’s Leap strain. In addition, X. fastidiosa Pnp does not show enzyme activity characteristic of that of a purine nucleoside phosphorylase.