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Pathogenesis-related protein-1a (PR-1a) is a protein of unknown function that is strongly induced during the onset of systemic acquired resistance (SAR) in tobacco. The expression of PR-1a is under complex regulation that is controlled at least partially by the rate of transcription. In this study, we demonstrated that 661 bp of 5' flanking DNA was sufficient to impart tobacco mosaic virus and salicylic acid inducibility to a reporter gene. The PR-1a promoter did not respond significantly to treatments with either auxin or cytokinin. Experiments with the protein synthesis inhibitor cycloheximide indicated that protein synthesis is required for salicylate-dependent mRNA accumulation. At flowering, the PR-1a gene was expressed primarily in the mesophyll and epidermal tissues of the leaf blade and the sepals of the flower. Several artifacts, most importantly ectopic expression in pollen, were associated with the use of the …