GENOME-WIDE IDENTIFICATION OF RAPIDLY EVOLVING GENES IN XYLELLA FASTIDIOSA: KEY ELEMENTS IN THE SYSTEMATIC IDENTIFICATION OF HOST STRAINS, AND IN THE SEARCH FOR PLANT-HOST PATHOGENICITY CANDIDATE GENES

• Author(s): Luck, Robert; Nunney, Leonard; Cooksey, Donald;
• Abstract: Xylella fastidiosa is not only a bacterium that causes Pierce's disease (PD) of grapevines. It also has a number of genetically distinct host strains (see Hopkins 1989). These strains show varying levels of cross-host pathogenicity. For example, PD strains do not infect peach, and phony peach disease strains do not infect grapevines. Similarly, the strains causing oleander leaf scorch (OLS) do not cause PD in grapevines or cause infectious symptoms in a number of other species (Purcell et al. 1999). The lack of cross-host infection means that genetic differences among the strains must encode the causes of hostspecific pathogenicity. Identifying the genes responsible for host-specific effects is an important step in understanding how infection might be controlled. The genetic differences determining host-specific adaptations are probably only a small fraction of the total genetic differences between the strains. To facilitate identifying host-specificity candidate genes, we need some initial filter that selects those genes most likely to be involved in host adaptation from among the approximately 2700 genes carried by X. fastidiosa. To this end, genomic research provides us with some extraordinarily powerful new tools for solving this kind of applied problem. It is self-evident that adaptive evolution depends upon changes in specific genes. In some cases, a single base substitution in a gene may be sufficient; however, such simple changes recur repeatedly in bacterial populations. The apparent separation of X. fastidiosa into stable host strains suggests host adaptations involve more complex changes. For this reason, we believe that the genes involved in host adaptation will be among those exhibiting the most rapid evolutionary change.
• Publication Date: Dec 2002
• Journal: 2002 Pierce's Disease Research Symposium