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): Nunney, Leonard; Luck, Robert; Stouthamer, R;
• Abstract: Genomic research provides an extraordinarily powerful new tool for solving applied problems. It can be extremely effective at resolving evolutionary relationships and can be used to extend earlier work defining the interrelationships of the plant-host strains of Xylella fastidiosa (see Hendson et al. 2001). Similarly, it can provide effective methods for identifying these host strains. Unambiguous identification is of considerable importance for understanding the epidemiology of Pierces disease and the other plant diseases caused by this bacterium. This has been approached using a variety of DNA based methods (Banks et al. 1999; Hendson et al. 2001; Rodrigues et al. 2003; Meinhardt et al. 2003;); however, an effective methodology for identifying the plant-host strains, including when they are mixed together, has yet to be developed. The availability of sequenced genomes allows us to analyze the evolutionary history of not just one or two genes, but of all of the genes that make up this bacterium. In particular, evolutionary genomic techniques developed to detect the action of natural selection (Yang 1998) provide a new approach to identifying genes important in plant-host specificity. The bacterium X. fastidiosa is generally assumed to be clonal. However, horizontal transfer of genes must occur given the presence of unique regions of DNA in the different host strains (Van Sluys et al. 2003). Such transfers are assumed to be virally mediated. The possibility of direct inter-strain genetic transfer is more difficult to detect, but needs to be investigated for two important reasons. First, bacteria from different strains are expected to mix at high density within the insect vector, and second, if such transfer does occur, it could lead to the very rapid evolution of novel pathogenic forms. Studying the details of sequence evolution across many genes provides information on the past occurrence of such events and hence their future likelihood.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium