TMV-induced expression of tobacco β-glucanase promoter activity is mediated by a single, inverted, GCC motif

Tobacco basic β-1,3-glucanase has been implicated in plant development and defense responses against pathogens. We examined the functional cis- elements involved in the response of basic β-1,3-glucanase promoter (gglb50) to infection with tobacco mosaic virus (TMV). In plants transformed with chimeric gglb50-β-glucuronidase (GUS) reporter gene, significant GUS- activity levels were measured in the leaves and in roots. Activity in the leaves was further induced (10-fold) by TMV infection. Maximal virus-induced activity was directed by a promoter region between -1233 to + 19 (gglb- 1233). A 5' deletion to -1038, which removed two TAAGAGCCGCC motifs (GCC- boxes), reduced virus-induced activity. However, when the gglb-1233 promoter was mutated by base substitutions within a third, inverted, GCC-box located between positions - 106 and -95, virus-induced promoter activity was abolished. Duplication of a small region containing this inverted GCC-box in the context of the gglb-1233 promoter resulted in increased virus-induced activity. Gel retardation assay demonstrated nuclear-factor binding to the inverted GCC-box. These studies strongly suggest the inverted GCC-box as a regulatory element essential for TMV-induced activity directed by the gglb50 promoter.