CONTRIBUTION OF XYLELLA FASTIDIOSA GENES UNIQUE TO GRAPE STRAINS TO ITS VIRULENCE TO GRAPE AND UTILITY IN SPECIFIC DETECTION OF GRAPE STRAINS BY DNA-BASED METHODS

• Author(s): Lindow, Steven; Feil, William;
• Abstract: Xylella fastidiosa (Xf) is a group of genetically similar strains that infect a wide range of plants. We hypothesized that discrete genetic factors among the very similar strains determine the ability of a strain to infect a particular host plant. To better understand what makes grape a good host for all grape strains but not for strains such as oleander and almond that cannot colonize grape, we conducted experiments to look for host specific genes of the grape strain. Through our microarray and in silico genomic studies, we have identified 20 potential Xf grape strain virulence genes. Of these, we have focused on 10 genes. We excluded 10 genes based on criteria such as they are phage related, DNA modification genes, part of a repeated gene complex, or are predicted house keeping genes, and thus not likely to have a role in plant virulence. It was clear from our studies that the microarray studies have produced fewer unique genes (genes present in one strain and lacking in another) to grape strains than expected, indicating that the identity between Xf Temecula and other non-grape strains must be closer than expected. Our in silico comparisons also revealed a high level of identity between grape and non-grape strains of Xylella. Because of this, we are now using dual labeling with our microarray studies to determine even small differences in gene sequence rather than simple lack of a particular gene. This is a more sensitive way to determine qualitative differences between the strains. We have now made knock-out mutants for seven of the 10 genes unique to grape strains that we expect to be most likely involved in virulence to grape. We used constructs that have a Kanamycin gene inserted near the 5 end of the gene for optimum efficiency in knocking out a given gene while preventing partial transcripts to be made in such knockout strains. Inoculation studies with grape have shown that several of these genes confer the ability to move within grape and thus to incite disease at sites away from the point of inoculation. The growth of these mutant strains in grape near the point of inoculation was not usually impaired, suggesting that such traits are involved specifically in other aspects of movement and symptom development in grape.
• Publication Date: Nov 2006
• Journal: 2006 Pierce's Disease Research Symposium