The molecular and enzymatic basis of bitter/non-bitter flavor of citrus fruit: Evolution of branch-forming rhamnosyltransferases under domestication

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The molecular and enzymatic basis of bitter/non-bitter flavor of citrus fruit: Evolution of branch-forming rhamnosyltransferases under domestication

Year: 

2013

Source of publication :

Plant Journal

Authors :

אופיר, רון

;

איל, יורם

;

ויסברג, מירה

;

ליברמן, רעיה

;

ספיר-מיר, מיה

;

פרידמן, אהובה

.

Volume :

Co-Authors: 

Frydman, A., Institute of Plant Sciences, Volcani Center, PO Box 6, Bet-Dagan, 50250, Israel
Liberman, R., Institute of Plant Sciences, Volcani Center, PO Box 6, Bet-Dagan, 50250, Israel
Huhman, D.V., Plant Biology Division, Samuel Roberts Noble Foundation, PO Box 2180, Ardmore, OK 73402, United States
Carmeli-Weissberg, M., Institute of Plant Sciences, Volcani Center, PO Box 6, Bet-Dagan, 50250, Israel
Sapir-Mir, M., Institute of Plant Sciences, Volcani Center, PO Box 6, Bet-Dagan, 50250, Israel
Ophir, R., Institute of Plant Sciences, Volcani Center, PO Box 6, Bet-Dagan, 50250, Israel
Sumner, L.W., Plant Biology Division, Samuel Roberts Noble Foundation, PO Box 2180, Ardmore, OK 73402, United States
Eyal, Y., Institute of Plant Sciences, Volcani Center, PO Box 6, Bet-Dagan, 50250, Israel

From page: 

166

To page: 

178

(

Total pages: 

13

)

Link :

The molecular and enzymatic basis of bitter/non-bitter flavor of citrus fruit: Evolution of branch-forming rhamnosyltransferases under domestication

Abstract: 

Domestication and breeding of citrus species/varieties for flavor and other characteristics, based on the ancestral species pummelo, mandarin and citron, has been an ongoing process for thousands of years. Bitterness, a desirable flavor characteristic in the fruit of some citrus species (pummelo and grapefruit) and undesirable in others (oranges and mandarins), has been under positive or negative selection during the breeding process of new species/varieties. Bitterness in citrus fruit is determined by the composition of branched-chain flavanone glycosides, the predominant flavonoids in citrus. The flavor-determining biosynthetic step is catalyzed by two branch-forming rhamnosyltransferases that utilize flavanone-7-O-glucose as substrate. The 1,2-rhamnosytransferase (encoded by Cm1,2RhaT) leads to the bitter flavanone-7-O-neohesperidosides whereas the 1,6-rhamnosytransferase leads to the tastelessflavanone-7-O-rutinosides. Here, we describe the functional characterization of Cs1,6RhaT, a 1,6-rhamnosyltransferase-encoding gene directing biosynthesis of the tasteless flavanone rutinosides common to the non-bitter citrus species. Cs1,6RhaT was found to be a substrate-promiscuous enzyme catalyzing branched-chain rhamnosylation of flavonoids glucosylated at positions 3 or 7. In vivo substrates include flavanones, flavones, flavonols and anthocyanins. Cs1,6RhaT enzyme levels were shown to peak in young fruit and leaves, and gradually subside during development. Phylogenetic analysis of Cm1,2RhaT and Cs1,6RhaT demonstrated that they both belong to the branch-forming glycosyltransferase cluster, but are distantly related and probably originated separately before speciation of the citrus genome. Genomic data from citrus, supported by a study of Cs1,6RhaT protein levels in various citrus species, suggest that inheritance, expression levels and mutations of branchforming rhamnosyltransferases underlie the development of bitter or non-bitter species/varieties under domestication. © 2012 The Authors.