Identification of a salicylic acid-responsive element in the promoter of the tobacco pathogenesis-related beta-1,3-glucanase gene, PR-2d.

The tobacco pathogenesis-related PR-2d gene encodes an acidic beta-1,3-glucanase. Expression of the PR-2d: uidA(GUS) chimeric gene is induced in leaves undergoing the hypersensitive resistance response to tobacco mosaic virus and after treatment with salicylic acid (SA), a chemical believed to play an important role(s) in disease resistance. We have constructed transgenic tobacco plants which carry various segments of the PR-2d promoter fused to a heterologous core 35S promoter driving the uidA(GUS) reporter gene. Their analysis indicates that sequences from -364 to -288 upstream of the PR-2d transcription start site confer a high level of activation by SA (20-fold). Mutations within this sequence, located between -339 and -333, depressed SA activation. This region is also required for the SA-inducibility of a truncated PR-2d:GUS chimeric gene. Contained within this region is a 25 bp element located between -348 and -324 which was specifically recognized by nuclear factors from tobacco leaves. No conclusive differences were observed in the ability of proteins in nuclear extracts from water-treated versus SA-treated plants to bind to this cis element in vitro.