Identification of a novel pathogen-responsive element in the promoter of the tobacco gene HSR203J, a molecular marker of the hypersensitive response.

The tobacco gene, HSR203J, which is specifically activated during the early steps of incompatible plant/pathogen interactions has been shown to be a molecular marker of the hypersensitive response (HR). It constitutes an ideal model for the identification of HR-responsive cis-regulatory elements. As a first step in the promoter dissection, deletion mutants of the 5' flanking sequence of HSR203J fused to the GUS reporter gene were analyzed. Then, the construction and study of chimeric constructs containing HSR203J promoter fragments fused to a minimal promoter enabled us to identify a 28-bp regulatory element located between -106 and -79 upstream of the transcription initiation site. This element has been shown to be necessary and sufficient for transcriptional activation in response to pathogen. It contains a 10-bp palindrome followed by its imperfect repeat. The mutagenesis of these two sequence elements led to the identification of a 12-bp motif termed HSRE (HSR203 responsive element) responsible for the marked induction of the HSR203J gene during the HR. Since this DNA region did not show any homology with known regulatory sequences, this 12 bp motif corresponds to a novel cis-regulatory element.