REGULATION OF SESQUITERPENE CYCLASE GENE-EXPRESSION - CHARACTERIZATION OF AN ELICITOR-INDUCIBLE AND PATHOGEN-INDUCIBLE PROMOTER

The promoter for a tobacco (Nicotiana tabacum) sesquiterpene cyclase g ene, a key regulatory step in sesquiterpene phytoalexin biosynthesis, has been analyzed. The EAS4 promoter was fused to the beta-glucuronida se (GUS) reporter gene, and the temporal and spatial expression patter ns of GUS activity were examined in stably transformed plants and in t ransient expression assays using electroporated protoplasts of tobacco . No GUS activity was observed in any tissues under normal growth cond itions. A low level of GUS activity was detected in wounded leaf, root , and stem tissues, whereas a much higher level was observed when thes e tissues were challenged with elicitors or microbial pathogens. The G US expression pattern directed by the EAS4 promoter was identical to t he induction patterns observed for the endogenous sesquiterpene cyclas e genes. Neither exogenous salicylic acid nor methyl jasmonate induced GUS expression; and H2O2 induced GUS expression to only a limited ext ent. Although the EAS4 promoter contains cis-sequences resembling prev iously identified transcriptional control motifs, other cis-sequences important for quantitative and qualitative gene expression were identi fied by deletion and gain-of-function analyses. The EAS4 promoter diff ers from previously described pathogen-/elicitor-inducible promoters b ecause it only supports inducible gene expression and directs unique s patial expression patterns.