THE UPSTREAM REGION OF THE GENE FOR THE PATHOGENESIS-RELATED PROTEIN 1A FROM TOBACCO RESPONDS TO ENVIRONMENTAL AS WELL AS TO DEVELOPMENTAL SIGNALS IN TRANSGENIC PLANTS

Pathogenesis-related proteins (PR proteins) are a heterogeneous group of proteins which are induced in plants by diverse stimuli, e.g. PR proteins are elicited by pathogen attack in the course of the hypersensitive defense reaction of the plant. To examine the regulation of these genes, the 5'-flanking region of the tobacco (Nicotiana tabacum cv. Wisconsin 38) PR-1a gene up to position -1533 was isolated from genomic DNA by the polymerase chain reaction. Two chimeric gene constructs containing 1533 bp and 906 bp, respectively, of the PR-1a upstream region fused to the GUS reporter gene were stably integrated into the tobacco genome. All primary transformants exhibited induced expression of the reporter gene after infection of the plants with tobacco mosaic virus or treatment with acetylsalicylic acid. In addition, similar expression of the reporter gene was observed in leaves of adult transgenic plants without any prior inductive treatments. To study this phenomenon in more detail, the F1 progeny of independent transgenic lines were monitored during the ontogeny of the plants. In normally developing tobacco plants, strong GUS activities were typically detected approximately 12 weeks after germination in the lowest leaves of vegetative plants. When successive leaves of individual plants were tested during the following weeks, a clear gradient of reporter gene activity had developed in the green leaves including the sepals from the bottom to the top of the plants. In all cases analyzed, this gradient of reporter gene expression was strictly parallelled by the expression of the endogenous PR-1 proteins. These results suggest that the acidic PR-1 proteins from tobacco fulfill a role during the later stages of plant development and that the PR-1a upstream region -906 to -335 contains positive regulatory elements for both environmental and developmental signals.