Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 10/12/2006
Publication Date: 11/27/2006
Citation: Labavitch, J.M., Backus, E.A., Morgan, D. 2006. The contribution of the pectin-degrading enzyme polygalacturonase (PG) in transmission of X. Fastidiosa to grape and the use of PG-inhibiting proteins for transgenic resistance to Pierce's Disease [abstract]. CDFA Pierce's Disease Control Program Research Symposium Proceedings. p. 287 Interpretive Summary: Previous work has shown that polygalacturonase inhibitor proteins (PGIPs) genetically engineered for expression in grapevine protect the plants against Pierce’s Disease (PD). This year, we began to reveal the reason for this. We showed that polygalacturonase (PG) secreted by Xylella fastidiosa (Xf) acts by degrading the structural components within the cell wall. Also PG, in combination with a bacterial beta-1,4-glucanase enzyme (BGase), disrupts xylem pit membranes that serve as barriers to spread of bacteria throughout the plant. Thus, both of these bacterial enzymes are crucial to the infection process, and if their action is inhibited, infection will be limited. We also report on set-backs that have slowed examination of the roles of insect plant cell wall-degrading enzymes in PD development. Fortunately, the set-backs are now being corrected.
Technical Abstract: Work this year has shown that polygalacturonase (PG) of Xylella fastidiosa (Xf) is an endo-acting enzyme. This provides a reference that can now be used to biochemically characterize the interaction between the pathogen’s PG and PG inhibitor proteins (PGIPs) that is implied by the fact that transgenic expression of PGIPs protects vines against Pierce’s Disease (PD). We also report that PG, in combination with a bacterial '-1,4-glucanase enzyme (BGase) disrupts xylem pit membranes that serve as barriers slowing systemic spread of bacteria. We also report on set-backs that have slowed examination of the roles of insect plant cell wall-degrading enzymes in PD development. Fortunately, the set-backs are now being corrected so that important questions can be addressed in work supported by a no-cost extension.