THE DEVELOPMENT OF PIERCES DISEASE IN XYLEM: THE ROLES OF VESSEL CAVITATION, CELL WALL METABOLISM, AND VESSEL OCCLUSION

• Author(s): Greve, Carl; Labavitch, John; Matthews, Mark;
• Abstract: This proposal is directed toward discovering the plant responses to infection that are fundamental to the progression of Pierce's disease (PD) in grapevine. The disease is caused by the growth of the bacterium Xylella fastidiosa (X.f.) in the xylem vessels of stems, petioles and leaf blades. The disease progresses rapidly, causing severe water deficits in infected shoots and vine deathoften within two years. However the progression of the disease and the mechanism(s) by which the disease produces water deficits and death in infected tissues have not been well established. The prevailing notion is that vessels become occluded with bacteria or products of metabolism. However, it is unclear how the bacterium moves through and between vessels, whether vessels cavitate upon introduction of the bacterium by the insect vector or artificial inoculation, and whether PD symptoms can be found in tissues at a distance from local concentrations of bacteria. The bacterium is reported to be larger than the openings in pit pore "membranes." Thus, it is likely that cell wall digestion is necessary for movement of the bacteria through the vine. This digestion may be a key component of disease progression. The studies in our project are designed to test the following hypothetical model of the events contributing to the development of PD. X.f. introduction to vesselsvessel cavitation initial water deficit X.f. population increase production of enzymes by X.f. (signals ?) cell wall digestion oligosaccharide signals ethylene synthesis rise a "wave" of vessel occlusion beyond the infection site global collapse of vine water transport leaf abscissionvine death
• Publication Date: Dec 2002
• Journal: 2002 Pierce's Disease Research Symposium