BIOLOGY OF THE XYLELLA FASTIDIOSA-VECTOR INTERFACE Project Leader

The Gram-negative bacterium Xylella fastidiosa (Xf) is the causal agent of many economically important plant diseases. This bacterium attaches to, multiplies in, and is inoculated from the foregut of sharpshooter leafhoppers, which feed on plant xylem sap. Little is known about the specific interactions between Xf cells and its vectors' foregut. Constituents of the foregut include mucopolysaccharides, chitin, proteins and other components. We have developed an in vitro assay to study the attachment of Xf to carbohydrates using nitrocellulose membranes coated with different polysaccharides. We found that Xf cells attach to polysaccharides that contain a chain of glucose or N-acetylglucosamine. These results suggest that the attachment of Xf cells to surfaces may be carbohydrate mediated. Xf cells treated with either protease K or pronase showed less attachment to the polysaccharides tested. Competition experiments with different sugars and lectins suggest that attachment of Xf to vector's foregut is carbohydrate mediated and that proteins of Xf may work as lectins that have affinity to sugars, especially glucose and N-acetylglucosamine. In order to identify carbohydrate binding proteins in Xf, we have studied the attachment of 15 different mutants to foregut extracts and different polysaccharides blotted in nitrocellulose membranes. Only hemagglutinin-like protein mutants exhibited less attachment. Insect transmission tests for the different mutants were also done; we found a correlation between the in vitro attachment assays and vector transmission to plants of the mutants tested.