title: The role of enoyl reductase genes in phloridzin biosynthesis in apple.
abstract: Phloridzin is the predominant polyphenol in apple (Malus × domestica Borkh.) where it accumulates to high concentrations in many tissues including the leaves, bark, roots and fruit. Despite its relative abundance in apple the biosynthesis of phloridzin and other related dihydrochalcones remains only partially understood. The key unidentified enzyme in phloridzin biosynthesis is a putative carbon double bond reductase which is thought to act on p-coumaroyl-CoA to produce the dihydro-p-coumaroyl-CoA precursor. A functional screen of six apple enoyl reductase-like (ENRL) genes was carried out using transient infiltration into tobacco and gene silencing by RNA interference (RNAi) in order to determine carbon double bond reductase activity and contribution to foliar phloridzin concentrations. The ENRL-3 gene caused a significant increase in phloridzin concentration when infiltrated into tobacco leaves whilst a second protein ENRL-5, with over 98% amino acid sequence similarity to ENRL-3, showed p-coumaroyl-CoA reductase activity in enzyme assays. Finally, an RNAi study showed that reducing the transcript levels of ENRL-3 in transgenic 'Royal Gala' led to a 66% decrease in the concentration of dihydrochalcones in the leaves in the one available silenced line. Overall these results suggest that ENRL-3, and its close homolog ENRL-5, may contribute to the biosynthesis of phloridzin in apple.
authors.affiliation: The New Zealand Institute for Plant and Food Research Ltd, Private Bag 92169, Auckland 1141, New Zealand. Electronic address: adare@plantandfood.co.nz.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Dare
authors.forename: Sumathi
authors.initials: S
authors.lastname: Tomes
authors.forename: Janine M
authors.initials: JM
authors.lastname: Cooney
authors.forename: David R
authors.initials: DR
authors.lastname: Greenwood
authors.forename: Roger P
authors.initials: RP
authors.lastname: Hellens
mesh_terms: D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D027845:Malus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010695:Phlorhizin / Q000096:biosynthesis* / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D010695:Phlorhizin; D010088:Oxidoreductases
keywords: Arabidopsis thaliana myeloblastosis transcription factor 75; AtMYB75; ENRL; Enoyl-ACP reductase; HPLC; Malus × domestica; Phloridzin; RNA interference; RNAi; Transient assay; enoyl reductase-like; high performance liquid chromatography