Characterization of an Elicitor- and Pathogen-lnducible Promoter

The promoter for a tobacco (Nicofiana tabacum) sesquiterpene cyclase gene, a key regulatory step in sesquiterpene phytoalexin biosynthesis, has been analyzed. The EAS4 promoter was fused to the P-glucuronidase (CUS) reporter gene, and the temporal and spatial expression patterns of C U S activity were examined in stably transformed plants and in transient expression assays using electroporated protoplasts of tobacco. N o C U S activity was observed in any tissues under normal growth conditions. A low level of C U S activity was detected in wounded leaf, root, and stem tissues, whereas a much higher level was observed when these tissues were challenged with elicitors or microbial pathogens. l h e CUS expression pattern directed by the EAS4 promoter was identical to the induction patterns observed for the endogenous sesquiterpene cyclase genes. Neither exogenous salicylic acid nor methyl iasmonate induced C U S expression; and H,O, induced GUS expression to only a limited extent. Although the EAS4 promoter contains cissequences resembling previously identified transcriptional control motifs, other cis-sequences important for quantitative and qualitative gene expression were identified by deletion and gain-offunction analyses. The EAS4 promoter differs from previously described pathogen-/elicitor-inducible promoters because it only supports inducible gene expression and directs unique spatial expression patterns.