Functional characterization of two p-coumaroyl ester 3'-hydroxylase genes from coffee tree: evidence of a candidate for chlorogenic acid biosynthesis.

Laboratoire de Génomique et Qualité du café, IRD, UMR 1097 DGPC, 911 Avenue Agropolis, BP 64501, 34394, Montpellier cedex 5, France.
Plant Molecular Biology (Impact Factor: 4.07). 06/2007; 64(1-2):145-59. DOI: 10.1007/s11103-007-9141-3
Source: PubMed

ABSTRACT Chlorogenic acid (5-CQA) is one of the major soluble phenolic compounds that is accumulated in coffee green beans. With other hydroxycinnamoyl quinic acids (HQAs), this compound is accumulated in particular in green beans of the cultivated species Coffea canephora. Recent work has indicated that the biosynthesis of 5-CQA can be catalyzed by a cytochrome P450 enzyme, CYP98A3 from Arabidopsis. Two full-length cDNA clones (CYP98A35 and CYP98A36) that encode putative p-coumaroylester 3'-hydroxylases (C3'H) were isolated from C. canephora cDNA libraries. Recombinant protein expression in yeast showed that both metabolized p-coumaroyl shikimate at similar rates, but that only one hydroxylates the chlorogenic acid precursor p-coumaroyl quinate. CYP98A35 appears to be the first C3'H capable of metabolising p-coumaroyl quinate and p-coumaroyl shikimate with the same efficiency. We studied the expression patterns of both genes on 4-month old C. canephora plants and found higher transcript levels in young and in highly vascularized organs for both genes. Gene expression and HQA content seemed to be correlated in these organs. Histolocalization and immunolocalization studies revealed similar tissue localization for caffeoyl quinic acids and p-coumaroylester 3'-hydroxylases. The results indicated that HQA biosynthesis and accumulation occurred mainly in the shoot tip and in the phloem of the vascular bundles. The lack of correlation between gene expression and HQA content observed in some organs is discussed in terms of transport and accumulation mechanisms.

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    ABSTRACT: Demand among consumers for fruits and vegetables with improved contents in bioactive compounds is increasing. In particular, a lot of attention is being paid to phenolic compounds, as they have been reported to present many beneficial effects for human health. However, oxidation of phenolic compounds present in the tissues of fruits and vegetables by polyphenol oxidases (PPOs) can result in browning, which affects negatively the quality of the produce. Eggplant (Solanum melongena) presents a high content in phenolics, in particular chlorogenic acid (CGA), which confers nutraceutical properties to this crop. In order to obtain information relevant for the development of varieties with high content in CGA and low browning, we have studied the diversity for CGA, PPO activity, and fruit flesh browning and their relationships in a collection of 18 Spanish accessions of eggplant. Also, using an interspecific mapping population between S. melongena and S. incanum we have mapped the genes involved in the synthesis pathway of CGA as well as the eggplant PPO genes. The results confirmed that eggplant presents high levels of CGA, and that a wide diversity exists for the three traits studied. Low levels of correlation have been found between CGA and PPO activity on one side and browning on the other, indicate that PPO is not a limiting factor in browning in the germplasm collection studied. The six genes of the pathway for the synthesis of CGA from phenylalanine have been mapped to five different linkage groups. Only two of the genes are linked indicating that selection of materials with the alleles favourable of different parents will be easily achieved. However, the five PPO genes mapped (PPO1 to PPO5) cluster together in the same linkage group, which will difficult obtaining recombinants. Mapping of these genes is of interest for marker assisted selection for high content in CGA and reduced browning. Overall, the results indicate that selection of eggplant varieties with high content in CGA and low browning is feasible. The information obtained is also useful for the genetic improvement of other fruits and vegetables in order to develop new cultivars with increased added value resulting from high content in phenolics and low browning.
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