Unraveling the first Xylella fastidiosa subsp. fastidiosa genome from Texas

Xylella fastidiose Wells et al. is a gram-negative bacterial plant pathogen spread by sharpshooter insect vectors including the glassy-winged sharpshooter, Homoladisce vitripennis (Germar). Pierce's disease of grapevines, Vitis vinifere L., is the result of the grape strain of the bacterium, X. festidiose subsp. festidiose growing in the xylem of the plant. Pierce's disease typically results in vine death within 1 to 2 years. Several X. festidiose subsp. festidiose isolates have been sequenced from California, but to understand the evolutionary history of the bacterium and pathogenicity differences between populations, it was the goal of this project to sequence a genome of the Texas grape strain, GB514. Whole genome shotgun titanium pyrosequencing was performed and resulting data assembled, yielding two primary contigs one of which was 2.49 megabases and represented what is predicted in this version 1 assembly to be a complete Xylelle chromosome. A second notable fragment did not assemble as part of the chromosome and could represent a possible low copy number plasmid or linear extrachromosomal DNA content. For the region that did not assemble, 39 novel genes have been identified with known functions. A BLASTn analysis of this gene collection found 94% query coverage and 98% identity to the recently uploaded plasmid pXF-RIV25 from mulberry isolate (X. festidiose subsp. multiplex). However, plasmid isolations of GB514, thus far, have not resulted in any detectable plasmid. Of the 39 genes identified, 11 genes code for the components of a functional Type IV secretion pathway (critical for many bacteria-infecting eukaryotic hosts). The presence of these Type IV genes integrated into the Texas grape strain or on a plasmid in two subspecies suggests it may have a critical role in virulence.