EXPRESSION PATTERNS OF AN ARABIDOPSIS PHENYLALANINE AMMONIA-LYASE PROMOTER IN TRANSGENIC TOBACCO

We have cloned and characterized one of the genes that encode phenylal anine ammonia-lyase from Arabidopsis thaliana. A 18-kb fragment contai ning the upstream region of this gene, PAL1, was transcriptionally fus ed to the beta-glucuronidase reporter gene, and the construct was intr oduced into tobacco by Agrobacterium, mediated leaf disc trans formati on. The distribution of beta-glucuronidase activity in the transgenic plants was analysed histochemically. The spatial pattern of activity s howed that the PAL1 promoter is very active in the vascular tissues. N o expression was observed in epidermal cells, trichomes and apical mer istems. Activation of the PAL1 promoter in the early stages of seedlin g development remained confined to the regions adjacent to the root ap ical meristems; in later stages of seedling development, the pattern o f expression was drastically altered. The results suggest that the PAL I promoter is under the control of a complex set of signal transductio n pathways which lead to its activation in response to tissue-specific , wounding and developmental cues.