THE PLANT CELL, Vol 5, Issue 9 1049-1062, Copyright © 1993 by American Society of Plant Biologists
Positive and Negative Regulatory Regions Control the Spatial Distribution of Polygalacturonase Transcription in Tomato Fruit Pericarp
J. Montgomery, V. Pollard, J. Deikman and R. L. Fischer
Department of Plant Biology, University of California, Berkeley, California 94720
The tomato fruit consists of a thick, fleshy pericarp composed
predominantly of highly vacuolated parenchymatous cells, which surrounds
the seeds. During ripening, the activation of gene expression results in
dramatic biochemical and physiological changes in the pericarp. The
polygalacturonase (PG) gene, unlike many fruit ripening-induced genes, is
not activated by the increase in ethylene hormone concentration associated
with the onset of ripening. To investigate ethylene
concentration-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
analysis indicated that a minimum of three promoter regions influence the
spatial regulation of PG transcription. A positive regulatory region from
-231 to -134 promotes gene transcription in the outer pericarp of ripe
fruit. A second positive regulatory region from -806 to -443 extends gene
activity to the inner pericarp. However, a negative regulatory region from
-1411 to -1150 inhibits gene transcription in the inner pericarp. DNase I
footprint analysis showed that nuclear proteins in unripe and ripe fruit
interact with DNA sequences within each of these three regulatory regions.
Thus, temporal and spatial control of PG transcription is mediated by the
interaction of negative and positive regulatory promoter elements,
resulting in gene activity in the outer pericarp but not the inner pericarp
of ripe tomato fruit. The expression pattern of PG suggests that, although
they are morphologically similar, there is a fundamental difference between
the parenchymatous cells within the inner and outer pericarp.
