TMV-INDUCED EXPRESSION OF TOBACCO BETA-GLUCANASE PROMOTER ACTIVITY ISMEDIATED BY A SINGLE, INVERTED, GCC MOTIF

Tobacco basic beta-1,3-glucanase has been implicated in plant developm ent and defense responses against pathogens. We examined the functiona l cis-elements involved in the response of basic beta-1,3-glucanase pr omoter (gglb50) to infection with tobacco mosaic virus (TMV). In plant s transformed with chimeric gglb50-beta-glucuronidase (GUS) reporter g ene, significant GUS-activity levels were measured in the leaves and i n roots. Activity in the leaves was further induced (10-fold) by TMV i nfection. Maximal virus-induced activity was directed by a promoter re gion between -1233 to +19 (gglb-1233). A 5' deletion to -1038, which r emoved two TAAGAGCCGCC motifs (GCC-boxes), reduced virus-induced activ ity. However, when the gglb-1233 promoter was mutated by base substitu tions within a third, inverted, GCC-box located between positions -106 and -95, virus-induced promoter activity was abolished. Duplication o f a small region containing this inverted GCC-box in the context of th e 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 reg ulatory element essential for TMV-induced activity directed by the ggl b50 promoter. (C) 1997 Elsevier Science Ireland Ltd.