Submitted to: Gene Expression
Publication Type: Abstract Only
Publication Acceptance Date: March 29, 1999
Publication Date: N/A
Technical Abstract: In plants, the process of abscission is characterized by localized cell separation and cell wall degradation in the area of organ detachment, known as the abscission zone. Associated with this precise and coordinated developmental event, which is initiated by ethylene and retarded by auxin, is an increase in the activity of numerous cell wall hydrolases including polygalacturonase and beta-1,4-glucanase (cellulase). Previous work in this laboratory resulted in the isolation of several genes coding for cell wall-degrading enzymes from bean (Phaseolus vulgaris), soybean (Glycine max) and tomato (Lycopersicon esculentum). Alignment of the gene promoters of the bean and soybean abscission cellulase genes revealed regions of high sequence similarity. Site directed mutagenesis has been used to create a series of mutations in these regions in the bean abscission cellulase (BAC) gene and the effect of the mutations assayed by transient expression in particle bombarded abscission zones. One region of particular interest includes the core motif (ACGT) for binding of basic leucine zipper (bZIP) transcription factors. Following mutation of this core sequence, an 80% decrease in expression of a luciferase reporter gene was observed, when compared to luciferase expression resulting from the unmutated control. Using this core bZIP-binding site as a target, we are currently embarking on a yeast one-hybrid screen of a bean abscission zone expression library in order to identify putative regulators of BAC gene transcription. An understanding of how abscission-related genes are regulated will provide potential areas for gene manipulation, with a view to controlling abscission processes in crop plants.