Ibdah, M., Institute of Biological Chemistry, Washington State University, PO Box 646340, Pullman, WA 99164-6340, USA, NeweYaar Research Center, Agriculture Research Organization, PO Box 1021, Ramat Yishay 30095, Israel
Berim, A., Institute of Biological Chemistry, Washington State University, PO Box 646340, Pullman, WA 99164-6340, USA
Martens, S., Fondazione Edmund Mach, Centro Ricerca e Innovazione, Department of Food Quality and Nutrition, Via E. Mach, 1 - 38010 San Michele all'Adige (TN), Italy
Valderrama, A.L.H., Fondazione Edmund Mach, Centro Ricerca e Innovazione, Department of Food Quality and Nutrition, Via E. Mach, 1 - 38010 San Michele all'Adige (TN), Italy
Palmieri, L., Fondazione Edmund Mach, Centro Ricerca e Innovazione, Department of Food Quality and Nutrition, Via E. Mach, 1 - 38010 San Michele all'Adige (TN), Italy
Lewinsohn, E., NeweYaar Research Center, Agriculture Research Organization, PO Box 1021, Ramat Yishay 30095, Israel
Gang, D.R., Institute of Biological Chemistry, Washington State University, PO Box 646340, Pullman, WA 99164-6340, USA
 

The apple tree (Malus sp.) is an agriculturally and economically important source of food and beverages. Many of the health beneficial properties of apples are due to (poly)phenolic metabolites that they contain, including various dihydrochalcones. Although many of the genes and enzymes involved in polyphenol biosynthesis are known in many plant species, the specific reactions that lead to the biosynthesis of the dihydrochalcone precursor, p-dihydrocoumaroyl-CoA (3), are unknown. To identify genes involved in the synthesis of these metabolites, existing genome databases of the Rosaceae were screened for apple genes with significant sequence similarity to Arabidopsis alkenal double bond reductases. Herein described are the isolation and characterization of a Malus hydroxycinnamoyl-CoA double bond reductase, which catalyzed the NADPH-dependent reduction of p-coumaroyl-CoA and feruloyl-CoA to p-dihydrocoumaroyl-CoA and dihydroferuloyl-CoA, respectively. Its apparent Km values for p-coumaroyl-CoA, feruloyl-CoA and NADPH were 96.6, 92.9 and 101.3 μM, respectively. The Malus double bond reductase preferred feruloyl-CoA to p-coumaroyl-CoA as a substrate by a factor of 2.1 when comparing catalytic efficiencies in vitro. Expression analysis of the hydroxycinnamoyl-CoA double bond reductase gene revealed that its transcript levels showed significant variation in tissues of different developmental stages, but was expressed when expected for involvement in dihydrochalcone formation. Thus, the hydroxycinnamoyl-CoA double bond reductase appears to be responsible for the reduction of the α,β-unsaturated double bond of p-coumaroyl-CoA, the first step of dihydrochalcone biosynthesis in apple tissues, and may be involved in the production of these compounds. © 2014 Elsevier Ltd. All rights reserved.