APPLICATION OF AGROBACTERIUM RHIZOGENES-MEDIATED TRANSFORMATION STRATEGIES FOR A RAPID HIGH THROUGHPUT SCREEN FOR GENETIC RESISTANCE TO PIERCES DISEASE IN GRAPE THAT MAINTAINS THE CLONAL INTEGRITY OF THE RECIPIENT HOST

• Author(s): Gilchrist, David; Kirkpatrick, Bruce; Lincoln, James; Walker, Andrew;
• Abstract: The goal of this project is to identify novel genes from either grape or heterologous plants that, when expressed in grape, will lead to disruption of infection, spread or symptom development of the xylem-limited bacteria, Xylella fastidiosa. There is no useful genetic resistance in commercially preferred grape clones, and introgression of resistance from grape relatives by sexual crossing introduces substantial genetic variation. Introgression of resistance would be most useful if it were introduced directly into vegetative tissue without requiring recurrent selection to attempt to return to the original host genotype. We have developed a functional screen for cDNAs that block either bacterial multiplication, movement or symptom expression using an Agrobacterium rhizogenes mediated transformation strategy. This system enables the direct introgression of cloned resistance genes into a susceptible host plant while maintaining the clonal integrity of the recipient plant following transformation. In working with symptomatic grape leaf tissue for isolation of RNA for development of cDNA libraries, we examined the pattern and form of symptom development cytologically. The cytological pattern of symptom development suggested a similarity to tissue death in other plant systems that we have been studying for several years. As a consequence of our preliminary cytological studies we concluded that the death that was occurring in the pre-symptomatic and symptomatic areas of leaves on infected plants borne changes that we associate with the activation of a programmed cell death process that exhibits the morphological hallmarks of apoptosis, a widely studied gene mediated fundamental process of development and disease in animals and in plants. We have therefore included as a second objective an examination of the molecular basis of cell death in pre-symptomatic and symptomatic tissues along with the immediate assessment of the effect of expressing anti-apoptotic transgenes in Pierces disease (PD) infected tissues on the development of death related symptoms in grape. The research plan includes a rapid functional screen for genes that confer resistance to PD in transformed grape tissue. The goal is to rapidly identify resistance genes in grape genotypes that block any one of several required steps in the infection and spread of X. fastidiosa in the xylem
• Publication Date: Dec 2002
• Journal: 2002 Pierce's Disease Research Symposium