Cloning and identification of the promoter of the tobacco Sar8.2b gene, a gene involved in systemic acquired resistance.

Expression of the Sar8.2 gene family is induced by salicylic acid (SA) in tobacco during induction of systemic acquired resistance. Expression of Sar8.2b, one member of this 12-member family, was detected as early as 12 h after treatment with SA and was maximal 36 h after SA treatment. In NahG transgenic tobacco plants, benzothiadiazole and dichloroisonicotinic acid induced expression of Sar8.2b but SA did not, suggesting that expression of the Sar8.2b gene is SA-dependent. Several putative cis-acting elements were found in the Sar8.2b gene promoter region, including an as-1 element and GT-1 and Dof binding sequences. We constructed a series of progressive deletion mutations in the Sar8.2b promoter region linked to the beta-glucuronidase (GUS) coding region and analyzed GUS activities by stable expression in transformants of Arabidopsis thaliana. Deletions between -728 and -927 bp or between -351 and -197 bp of the promoter region resulted in a significant reduction in GUS activity induced by SA treatment as shown in stable transformants of A. thaliana. The -197 bp fragment of the promoter region was found to confer a relatively low level of GUS activity induced by SA treatment in stable expression of transformants in A. thaliana. The results suggest that 927 bp of the Sar8.2b gene promoter confers full promoter activity and that cis-acting elements required for high-level SA-inducible expression of the Sar8.2b gene may exist within the regions -728 to -927 bp and -197 to -351 bp.