Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/13/2000
Publication Date: N/A
Citation: Interpretive Summary: Abscission is the process by which plants shed organs. The enzymes cellulase and polygalacturonase (PG) are important in breaking down the cell wall surrounding plant cells. The breakdown of the cell walls allows the cells to separate from each other and form the separation layer. In this manuscript we report the spatial distribution of two PGs in both the abscission zones and pistils of tomato. In addition, we propose a model for how the process of abscission is coordinated in many different types of cells. The purpose of this study is to better understand the regulation and expression of PG in tomato so that scientists and biotechnologists can use this information to genetically engineer plants with beneficial abscission properties (i.e., increased yield and quality).
Technical Abstract: The tomato polygalacturonase genes, TAPG1 and TAPG4, are abundantly expressed in both abscission zones and the pistils of mature flowers. To further investigate the spatial and temporal expression patterns for these genes, the TAPG gene promoters were ligated to beta-glucuronidase (GUS) reporter genes and transformed into tomato (Lycopersicon esculentum). GUS expression with both constructs was similar and entirely consistent with the expression patterns of the native gene transcripts. GUS activity was observed in the weakening abscission zones of the leaf petiole, flower and fruit pedicel, flower corolla, and fruit calyx. In leaf petiole and flower pedicel zones this activity was enhanced by ethylene and inhibited by IAA. 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 was more evenly distributed across the separation layer. Like the native genes, GUS was also expressed in the stigma. Activity was not apparent in pistils until the flowers had opened and was confined to the stigma and style immediately 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.