Citrus fruit bitter flavors: Isolation and functional characterization of the gene Cm1,2RhaT encoding a 1,2 rhamnosyltransferase, a key enzyme in the biosynthesis of the bitter flavonoids of citrus

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Citrus fruit bitter flavors: Isolation and functional characterization of the gene Cm1,2RhaT encoding a 1,2 rhamnosyltransferase, a key enzyme in the biosynthesis of the bitter flavonoids of citrus

Year: 

2004

Source of publication :

Plant Journal

Authors :

Eyal, Yoram

;

Frydman, Ahuva

;

Lewinsohn, Efraim

;

Weisshaus, Oori

.

Volume :

Co-Authors: 

Frydman, A., Institute of Horticulture, Volcani Center, ARO, PO Box 6, Bet-Dagan 50250, Israel
Weisshaus, O., Institute of Horticulture, Volcani Center, ARO, PO Box 6, Bet-Dagan 50250, Israel
Bar-Peled, M., Department of Plant Biology, Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602-4712, United States
Huhman, D.V., Plant Biology Division, Samuel Roberts Noble Foundation, PO Box 2180, Ardmore, OK 73402, United States
Sumner, L.W., Plant Biology Division, Samuel Roberts Noble Foundation, PO Box 2180, Ardmore, OK 73402, United States
Marin, F.R., Lab. de Cie. Y Tecn. de Alimentos, Facultad de Ciencias, Campus de Cantoblanco, Ctra de Colmenar, km 15, 28049 Madrid, Spain
Lewinsohn, E., Institute of Field Crops, Newe-Ya'Ar Research Center, ARO, Ramat-Yishay 30095, Israel
Fluhr, R., Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
Gressel, J., Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
Eyal, Y., Institute of Horticulture, Volcani Center, ARO, PO Box 6, Bet-Dagan 50250, Israel

From page: 

88

To page: 

100

(

Total pages: 

13

)

Link :

Citrus fruit bitter flavors: Isolation and functional characterization of the gene Cm1,2RhaT encoding a 1,2 rhamnosyltransferase, a key enzyme in the biosynthesis of the bitter flavonoids of citrus

Abstract: 

Species of the genus Citrus accumulate large quantities of flavanones that affect fruit flavor and have been documented to benefit human health. Bitter species, such as grapefruit and pummelo, accumulate bitter flavanone-7-O- neohesperidosides responsible, in part, for their characteristic taste. Non-bitter species, such as mandarin and orange, accumulate only tasteless flavanone-7-O-rutinosides. The key flavor-determining step of citrus flavanone-glycoside biosynthesis is catalyzed by rhamnosyltransferases; 1,2 rhamnosyltransferases (1,2RhaT) catalyze biosynthesis of the bitter neohesperidosides, while 1,6 rhamnosyltransferases (1,6RhaT) catalyze biosynthesis of the tasteless rutinosides. We report on the isolation and functional characterization of the gene Cm1,2RhaT from pummelo which encodes a citrus 1,2RhaT. Functional analysis of Cm1,2RhaT recombinant enzyme was conducted by biotransformation of the substrates using transgenic plant cell culture. Flavanones and flavones, but not flavonols, were biotransformed into 7-O-neohesperidosides by the transgenic BY2 tobacco cells expressing recombinant Cm1,2RhaT. Immunoblot analysis established that 1,2RhaT protein was expressed only in the bitter citrus species and that 1,6RhaT enzyme, whose activity was previously documented in non-bitter species, was not cross-reactive. Expression of Cm1,2RhaT at the RNA level was prominent in young fruit and leaves, but low in the corresponding mature tissue, thus correlating well with the developmental pattern of accumulation of flavanone-neohesperidosides previously established. Phylogenetic analysis of the flavonoid glycosyltransferase gene family places Cm1,2RhaT on a separate gene cluster together with the only other functionally characterized flavonoid-glucoside rhamnosyltransferase gene, suggesting a common evolutionary origin for rhamnosyltransferases specializing in glycosylation of the sugar moieties of flavonoid glucosides.