Submitted to: Plant Physiology
Publication Type: Abstract Only
Publication Acceptance Date: March 29, 1999
Publication Date: N/A
Technical Abstract: Abscission involves controlled degradation of cell wall material that leads to cell separation in a distinct layer of plant cells that comprise the area of organ detachment or abscission zone (AZ). Accompanying organ separation is an increase in the activity of several cell wall hydrolases including polygalacturonase and endo beta-1,4-glucanase (cellulase). Both ethylene and auxin are known to be important temporal regulators of abscission and hydrolase gene expression, however, information regarding the molecular genetic regulation of these cell wall-degrading enzymes is limited. Our primary objective is to investigate the underlying mechanisms controlling leaf abscission in bean by focussing on transcriptional regulation of an abscission-related cellulase gene. Previously, we identified abscission-related genes encoding cellulases from bean (Phaseolus vulgaris) and soybean (Glycine max). Comparison of the 5' upstream sequence of these genes revealed regions of high sequence similarity. Site-directed mutagenesis has been used to create a series of mutations in these regions of 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. We are currently using various methods, including yeast one hybrid screening and degenerate PCR, to identify factors which bind to the bZIP core sequence in the BAC gene promoter.