Analysis of gene promoters for two tomato polygalacturonases expressed in abscission zones and the stigma

The tomato (Lycopersicon esculentum ev Ailsa Craig) polygalacturonase genes TAPG1 (LYCes;Pga1;2) and TAPG4 (LYCes; Pga1;5) are abundantly expressed in both abscission zones and the pistils of mature flowers, To further invest igate the spatial and temporal expression patterns for these genes, the TAP G gene promoters were ligated to beta-glucuronidase (GUS) reporter genes an d transformed into tomato. GUS expression with both constructs was similar and entirely consistent with the expression patterns of the native gene tra nscripts. GUS activity was observed in the weakening abscission zones of th e leaf petiole, flower and fruit pedicel, flower corolla, and fruit calyx. In leaf petiole and flower pedicel zones this activity was enhanced by ethy lene and inhibited by indole-3-acetic acid. On induction of abscission with ethylene, GUS accumulation was much earlier in TAPG4:GUS than in TAPG1:GUS transformants. Moreover, TAPG4:GUS staining appeared to predominate in the vascular bundles relative to surrounding cortex cells whereas TAPG1:GUS wa s more evenly distributed across the separation layer. Like the native gene s, GUS was also expressed in the stigma. Activity was not apparent in pisti ls until the flowers had opened and was confined to the stigma and style im mediately proximal to it. A minimal promoter construct consisting of a 247- bp 5'-upstream element from TAPG1 was found to be sufficient to direct GUS expression in both abscission zones and the stigma.