Poster: Secondary metabolism

Abs # 250: Analysis of citrus plants transformed with flavonoid pathway Genes

Presenter:	Koca, Ufuk , ukoca@ifas.ufl.edu
Authors	Koca, Ufuk  (A)   Berhow,  Mark  (B)   Eyal, Yoram  (C)   Frydman, Ahuva  (C)   Moore, Gloria  (A)
Affiliations:	(A): University of Florida (B): USDA-REE-ARS-MWA-NCAUR-BAR, Peoria, IL 61604 (C): Volcani Institute, Bet Dagan, Israel.
Web Site:	http://www.hos.ufl.edu/mooreweb

Flavonoids are secondary metabolites, which display a variety of physiological effects in both plants and animals. They function mostly in protection from UV light; in scavenging of free radicals; in pollination and seed dispersal via their color features in plants. Their some of the known functions are anticarcinogenic, antioxidant, anti-inflammatory, anti-allergic and anti-mutagenic in animals. The major flavonoids in citrus are the flavanone glycosides, which are produced throughout the plant in high concentrations. These affect the taste rather than color. Flavanone rutinosides are tasteless, while flavanone neohesperidosides are bitter. Naringin is the major bitter compound in grapefruit. Bitter flavor not only diminishes the market value of the fruit and juice products but also deprives consumers of the nutritional benefit of them. Our main objective is to manipulate the biosynthesis of flavanone glycosides in citrus using molecular genetics and transformation techniques in order to decrease the bitter taste. To begin with, cDNAs of the structural genes chalcone synthase (CHS) and chalcone isomerase (CHI) were isolated from citrus. Sense and antisense constructs of these cDNAs were transferred to grapefruit to suppress the target gene expression and/or increase the nonbitter flavonoid compounds. We further transformed grapefruit with sense and hairpin (hp) forming constructs of the 1,2 rhamnosyl transferase (1,2 RT) cDNA, which catalyzes the last biochemical step in the production of naringin. Transformed plants are being evaluated for phenotype, their transgene copy numbers, and for their flavanone neohesperidoside expression levels via molecular techniques. They are also being evaluated for their flavonoid content by chromatographic methods.