Submitted to: Gordon Research Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: December 18, 2000
Publication Date: N/A
Ethylene-promoted leaf abscission in bean (Phaseolus vulgaris) involves localized induction of a gene encoding a beta-1,4-glucansase (cellulase) in addition to other cell wall hydrolases. Activity of the bean abscission cellulase (BAC) is limited specifically to the cells comprising the area of organ detachment, known as the abscission zone (AZ). Expression of the BAC mRNA is induced by ethylene after 24h exposure and repressed following treatment with auxin, an abscission inhibitor. Currently, molecular information regarding the control of abscission and regulation of genes encoding cell wall hydrolases is limited. Thus, analysis of the BAC 5' upstream sequence is the focus of our present study. Comparison of the BAC promoter sequence to its isolog in soybean (Glycine max) revealed regions of high sequence similarity. One region in particular comprised a core basic leucine zipper (bZIP) transcription factor binding site (ACGT). Following mutation of this core sequence, an 80% decrease in expression of a luciferase reporter gene was observed in transient assays when compared to luciferase expression from an unmutated control. Using this core bZIP-binding site as a target, we are currently embarking on a yeast one-hybrid screen of a bean AZ expression library in order to identify putative regulators of BAC gene transcription. In addition, five cDNAs encoding bZIP proteins were isolated from the AZ expression library by conventional screening. Our progress with the one-hybrid screen of both the entire library and the individual bZIP cDNAs will be presented.