ROLES OF XYLELLA FASTIDIOSA PROTEINS IN VIRULENCE

• Author(s): Bruening, George; Civerolo, Ed; Dandekar, Abhaya; Gupta, Goutam;
• Abstract: This work derives from a preliminary experiment by Civerolo and Bruening in which Chenopodium quinoa (Cq) was found to develop a localized chlorosis 24-48 hr after leaves were infiltrated with a suspension of live or heat-killed Xylella fastidiosa (Xf) cells. Excised electrophoresis gel regions were assayed for chlorosis-inducing activity, which was associated with a protein band with mobility corresponding to an estimated mass of 40K. Mass spectrometry of material the gel band revealed peptides corresponding to about 40% of the peptides predicted for the mopB gene. Xf mopB is an ompA protein. Members of the ompA group are located in the outer membrane of Gram-negative bacteria. The mopB translation product, signal peptide, and mature mopB protein were identified. In the present period, we showed that fluorescent anti-mopB IgG binds to intact Xf cells grown in liquid culture, confirming the location of mopB on the Xf cell surface. Previously we found that Xf cells extracted with SDS under specific conditions are depleted in most non-mopB proteins. This observation was extended by solubilizing mopB from the SDS-extracted cells at a slightly elevated pH, at 30C in the presence of SDS and sodium perchlorate. Only traces of other proteins contaminated the mopB preparation. We postulate that mopB, as the major outer membrane protein of Xf, may participate in an interaction between Xf and the xylem sites at which colonization of the plant by Xf is initiated. Understanding a mopB-xylem interaction could direct strategies for interfering with Xf infection of grape and other Xf hosts. We demonstrated that thin balsa wood squares are able to absorb mopB from a mixture of mopB with other proteins, in the presence of non-ionic detergents known to be effective in solubilizing integral membrane proteins. Cellulose, in the form of washed filter paper, was similarly selective. These results support, but do not prove, our hypothesis about a role for mopB in Xf infection, possibly acting to bind Xf to the xylem interior. It may be possible to exploit mopB as a target for controlling Pierces disease.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium