EVALUATION OF GENES ISOLATED BY A FUNCTIONAL GENETIC SCREEN FOR SUPPRESSION OF BACTERIAL GROWTH OR SYMPTOMS IN PIERCES DISEASE

• Author(s): Gilchrist, David; Lincoln, James;
• Abstract: Our overall objective is to identify genes from cDNA libraries of either grape or heterologous plants that, when up regulated in grape, will disrupt infection, spread or symptom development by the xylem-limited bacteria, Xylella fastidiosa (Xf). Hence, we are interested in the effect of the genetic disruption of Pierces disease (PD) symptoms on the movement or establishment of the bacterium in the xylem of susceptible grape plants. Recent published information from our laboratory established that specific transgenes from homologous or heterologous hosts that block programmed cell death (PCD) during plant disease development, can arrest both symptom development and microbial growth in planta in a range of plant-microbe interactions. A functional screen was used to evaluate cDNA libraries of grape and tomato for genes that, when overexpressed in tissues stimulated to undergo PCD, would block the death and therefore represent potential anti-PCD (anti-disease symptom) genes. Collectively, more than 500,000 cDNAs were screened and 12 genes were cloned that when overexpressed as transgenes in tomato or grape blocked PCD. Three of these genes when overexpressed as transgenes blocked PCD triggered by a verified ceramide-derived inducer of plant PCD. One of these gene, designated as PR1A in grape, was chosen for further direct characterization. This gene has high sequence homology to a gene family from humans, nematodes, hookworms and several plant species, wherein its expression is correlated with situations in which PCD is blocked in both animal and plant diseases. When overexpressed as a transgene in grape, the PCD sensitive grape tissues is now insensitive to microbial inducers of PCD. We believe that 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 PD infected tissues on the development of death-related symptoms in grape, will be very informative in the short run in terms of PD biology and physiology. In a longer time frame these data will likely yield genetic strategies for protection of grape against infection by Xf in years not decades.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium