BACTERIAL INDUCED ACTIVATION OF AN ARABIDOPSIS PHENYLALANINE AMMONIA-LYASE PROMOTER IN TRANSGENIC TOBACCO PLANTS

Two chimeric gene fusions of the Arabidopsis phenylalanine ammonia-lyase promoter (PAL1) with the beta-glucuronidase (GUS) reporter gene were introduced into tobacco (Nicotiana tabacum) plants for studying the functional properties of this promoter in response to bacterial infection. The distribution of GUS expression in the transgenic tobacco was highly similar to that of endogenous PAL1 transcripts in Arabidopsis. Infiltration of leaves of transgenic tobacco plants containing the PAL1-GUS gene fusion with Pseudomonas solanacearum strain K60 (compatible) or B1 (incompatible) resulted in a rapid activation of GUS expression. The temporal induction pattern elicited by B1 was characterized by a faster rise rate, and higher peak GUS activity than that by K60. A rapid drop in GUS activity was observed by 12 h in leaves infiltrated with B1 but not in those infiltrated with K60. Spatial pattern analysis revealed that GUS expression in the leaves infiltrated with B1 exhibited a spread pattern, while GUS expression in the leaves infiltrated with K60 remained localized. Infiltration of the transgenic tobacco leaves with heat-killed cells of K60 or B1 generated a massive and long-lived induction profile of GUS expression as compared to that in leaves infiltrated with live cells of K60 or B1. Our results suggest that operation of Arabidopsis PAL1 gene is conserved between Arabidopsis and tobacco. The expression pattern of the PAL1-GUS gene in tobacco may serve as an indicator for expression of the endogenous tobacco PAL gene.