2 CLASSES OF CIS SEQUENCES CONTRIBUTE TO TISSUE-SPECIFIC EXPRESSION OF A PAL2 PROMOTER IN TRANSGENIC TOBACCO

Genes encoding phenylalanine ammonia-lyase (PAL) are expressed in a co mplex pattern during plant development and in response to light, patho gen ingress, mechanical damage and other stresses. Analysis of the pro moter of the bean PAL2 gene in transgenic tobacco has shown that some regions responsible for developmental expression are functionally comp ensatory. The minimum sequence containing all cis sequences necessary for developmental patterns of expression is within -254 bp of the tran scription start site. Footprinting and electrophoretic mobility shift assay studies of this region revealed potential cis sequences which co incided with the functional domains defined by small deletions and pro moter fusions. Mutations in these potential cis sequences in the conte xt of the minimal -254 bp promoter altered tissue-specific expression patterns, confirming the importance of these sequences for expression in vivo. A functional model for the promoter is presented which predic ts that three AC-elements, which are possible Myb protein binding site s, together with a G-box, interact to direct the complex patterns of t issue-specific expression observed.