Isolation and characterization of a phenylalanine ammonia-lyase gene (PAL) promoter from Ginkgo biloba and its regulation of gene expression in transgenic tobacco plants

The Ginkgo biloba produces flavonoids and ginkgolides of high interest due to their medical values. Phenylalanine ammonia-lyase (PAL) is a core enzyme in the flavonoid biosynthesis pathway. In this study, we constructed genomic libraries with the DNA from leaves of 18-year-old grafts G. biloba. Using nested PCR method, a 1,627 bp 5' flanking region, named GbPALp (GenBank: GU968736) of a PAL gene (GbPAL) was isolated from genomic libraries, and the analysis of the promoter sequence by the PLACE database has revealed the existence of several putative cis-elements. To assess the organ-specificity and developmental characteristics of PAL gene expression in G. biloba, the GbPALp-driven GUS expression in transgenic tobacco was studied. Histological analysis of the transgenic young tobacco plants showed that the cloned PAL promoter displayed a tissue-specific GUS staining restricted to root hair region, the cortex of root, the vascular bundle cells, the cortex and the primary xylem of stems, and vascular region of leaves. In transgenic mature plant, GUS was expressed in the spire apical meristem of stems but not in leaves and root. The GUS activity in transgenic young tobacco leaves was also observed to be induced by a variety of stresses, including UV-B, abscisic acid, methyl jasmonate and salicylic acid, respectively. The results indicated that GbPALp had multiple functions in the expression under the various developmental stages and stress conditions in the transgenic tobacco.