Poster: Hormones

Abs # 627: Regulation of a Peach Type II Chlorophyll a/b-binding Protein Gene by Exogenous Ethylene

Presenter:	Gilkerson, Jonathan R, gilkerson3@marshall.edu
Authors	Gilkerson, Jonathan R (A)   Harrison, Marcia A (A)
Affiliations:	(A): Marshall University

A ripening fruit undergoes many processes including the production of ethylene, chlorophyll degradation, and a loss of flesh firmness. Chlorophyll catabolism is significant because of its economic importance related to shelf life and taste of the fruit. Ethylene indirectly controls this process by regulating genes coding for components associated with the two photosystems. Of these components, the chlorophyll a/b-binding (CAB) proteins have been most extensively studied. Because little research has been dedicated to a negative regulation mechanism, our objective is to elucidate transcriptional regulation of the CAB gene by ethylene. Deletions of the CAB gene promoter were engineered into the pUCAP vector for transient gene expression studies. Constructs were engineered with a CAB promoter fragment upstream of the reporter gene, b-glucuronidase (GUS), and GUS expression directed by the 35S promoter from cauliflower mosaic virus served as the control. Leaf tissue of Arabidopsis thaliana or tobacco was transformed with the promoter/reporter constructs using a particle bombardment system. Expression of the GUS gene in the presence or absence of exogenous ethylene was assayed by colorimetric and fluorometric analyses, and activity was confirmed using RT-PCR. Results of fluorometric assays demonstrate that the 600 bp CAB promoter/reporter construct show an expression level five times that of non-bombarded tissue. Results from bombardment with a 1600 bp promoter/reporter construct are similar to those of the short promoter construct. The colorimetric assays complement these results. A decrease in expression in transformed tissue exposed to ethylene compared to that in the absence suggests negative transcriptional control of the CAB gene by ethylene.