Expression of a PALI promoter luciferase gene fusion in Arabidopsis thaliana in response to infection by phytopathogenic bacteria

The Arabidopsis phenylalanine ammonia-lyase promoter (PALI), fused to the luciferase F (lux F) gene, was introduced into Arabidopsis thaliana plants, The temporal and spatial activities of the Arabidopsis PALI promoter were determined in transgenic Arabidopsis leaves infiltrated with avirulent and virulent strains of phytopathogenic Pseudomonas syringae. Luciferase activity was 3-4-fold higher in leaves infiltrated with P, syringae pathovar tomato (avirulent) than in uninfiltrated leaves; these increases were sustained for at least 24-72 h post-infiltration. In contrast, only small transient increases in luciferase activity lasting 24-48 h were observed in leaves infiltrated with P. syringae pv. maculicola (virulent), or 'mock-inoculated' with MgCl2. PALI-lux F expression was localized in the band of leaf-tissue surrounding the bacterial infiltration site and the hypersensitive lesion. The increased bioluminescence in leaves, measured in planta, correlated with the measurements of increased bioluminescence gathered in vitro using luminometry. This noninvasive luciferase reporter gene system will aid further studies of PALI promoter regulation in Arabidopsis.