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Summary

The tobacco pathogenesis-related PR-2d gene encodes an acidic β-1,3-glucanase. Expression of the PR-2d:uidA(GUS) chimeric gene is induced in leaves undergoing the hyper-sensitive 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.