Biochemical evidence of bacterial exopolysaccharide production in grapevines infected with Xylella fastidiosa, the causal agent of Pierces disease

• Author(s): Greve, Carl; Kirkpatrick, Bruce; Labavitch, John; Roper, M.; Stevenson, Joshua;
• Abstract: Xylella fastidiosa (Xf) colonizes xylem elements of grapevines and during this process the vessels become occluded. Tyloses originate from grapevine xylem parenchyma cells, but the origin of the occluding gels is unclear. Bacterial exopolysaccharide (EPS) could be a component of these gels. The X. f. genome sequence provides evidence that X. f. is capable of producing an EPS similar to xanthan gum produced by Xanthomonas spp. The genome-based EPS structure consists of a glucan backbone substituted with Man-GlcA disaccharide side chains. Gas Chromatography and Mass Spectrometry analysis of petiole tissue and xylem sap from X. f. infected grapevines showed a significantly higher content of GlcA and Man than controls. The extracts also showed elevated levels of Gal, GalA, and Ara, constituents of plant pectins. These data suggest that the occluding gels in X. f. infected grapevines probably consist of polysaccharides of both host and pathogen origin.
• Publication Date: Jun 2003
• Journal: Phytopathology