POSITIVE AND NEGATIVE REGULATORY REGIONS CONTROL THE SPATIAL-DISTRIBUTION OF POLYGALACTURONASE TRANSCRIPTION IN TOMATO FRUIT PERICARP

The tomato fruit consists of a thick, fleshy pericarp composed predomi nantly of highly vacuolated parenchymatous cells, which surrounds the seeds. During ripening, the activation of gene expression results in d ramatic biochemical and physiological changes in the pericarp. The pol ygalacturonase (PG) gene, unlike many fruit ripening-induced genes, is not activated by the increase in ethylene hormone concentration assoc iated with the onset of ripening. To investigate ethylene concentratio n-independent gene transcription in ripe tomato fruit, we analyzed the expression of chimeric PG promoter-beta-glucuronidase (GUS) reporter gene fusions in transgenic tomato plants. We determined that a 1.4-kb PG promoter directs ripening-regulated transcription in outer pericarp but not in inner pericarp cells, with a sharp boundary of PG promoter activity located midway through the pericarp. Promoter deletion analy sis indicated that a minimum of three promoter regions influence the s patial regulation of PG transcription. A positive regulatory region fr om -231 to -134 promotes gene transcription in the outer pericarp of r ipe fruit. A second positive regulatory region from -806 to -443 exten ds gene activity to the inner pericarp. However, a negative regulatory region from -1411 to -150 inhibits gene transcription in the inner pe ricarp. DNase I footprint analysis showed that nuclear proteins in unr ipe and ripe fruit interact with DNA sequences within each of these th ree regulatory regions. Thus, temporal and spatial control of PG trans cription is mediated by the interaction of negative and positive regul atory promoter elements, resulting in gene activity in the outer peric arp but not the inner pericarp of ripe tomato fruit. The expression pa ttern of PG suggests that, although they are morphologically similar, there is a fundamental difference between the parenchymatous cells wit hin the inner and outer pericarp.