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Plant Physiology Preview Published on January 27, 2006; 10.1104/pp.105.074955
Received November 30, 2005 Cinnamate metabolism in ripening fruit: Characterization of an UDP-glucose:cinnamate glucosyltransferase from strawberry (Fragaria x ananassa)
Biomolecular Food Technology, Technical University Munich, Lise-Meitner-Str. 34, 85354 Freising, Germany * Corresponding author; email: schwab{at}wzw.tum.de.
Strawberry fruits accumulate (hydroxy)cinnamoyl glucose esters which may serve as the biogenetic precursors of diverse secondary metabolites such as the flavor constituents methyl cinnamate and ethyl cinnamate. Here, we report on the isolation of a cDNA encoding an UDP-glucose: cinnamate glucosyltransferase (Fragaria x ananassa glucosyltransferase 2, FaGT2) from ripe fruit of Fragaria x ananassa cv. Elsanta that catalyzes the formation of 1-O-acyl-glucose esters of cinnamic acid, benzoic acid and their derivatives in vitro. QRT-PCR analysis indicated that FaGT2 transcripts accumulate to high levels during strawberry fruit ripening and to lower levels in flowers. The levels in fruits positively correlated with the in planta concentration of cinnamoyl, p-coumaroyl, and caffeoyl glucose. In leaf high amounts of glucose esters were detected but FaGT2 mRNA was not observed. The expression of FaGT2 is negatively regulated by auxin, induced by oxidative stress and by (hydroxy)cinnamic acids. Although FaGT2 glucosylates a number of aromatic acids in vitro, quantitative analysis in transgenic lines containing an antisense construct of FaGT2 under the control of the constitutive 35S CaMV promoter demonstrated that the enzyme is only involved in the formation of cinnamoyl glucose and p-coumaroyl glucose during ripening.
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