title: The Cer-cqu gene cluster determines three key players in a β-diketone synthase polyketide pathway synthesizing aliphatics in epicuticular waxes.
abstract: Aliphatic compounds on plant surfaces, called epicuticular waxes, are the first line of defense against pathogens and pests, contribute to reducing water loss and determine other important phenotypes. Aliphatics can form crystals affecting light refraction, resulting in a color change and allowing identification of mutants in their synthesis or transport. The present study discloses three such Eceriferum (cer) genes in barley - Cer-c, Cer-q and Cer-u - known to be tightly linked and functioning in a biochemical pathway forming dominating amounts of β-diketone and hydroxy-β-diketones plus some esterified alkan-2-ols. These aliphatics are present in many Triticeae as well as dicotyledons such as Eucalyptus and Dianthus. Recently developed genomic resources and mapping populations in barley defined these genes to a small region on chromosome arm 2HS. Exploiting Cer-c and -u potential functions pinpointed five candidates, of which three were missing in apparent cer-cqu triple mutants. Sequencing more than 50 independent mutants for each gene confirmed their identification. Cer-c is a chalcone synthase-like polyketide synthase, designated diketone synthase (DKS), Cer-q is a lipase/carboxyl transferase and Cer-u is a P450 enzyme. All were highly expressed in pertinent leaf sheath tissue of wild type. A physical map revealed the order Cer-c, Cer-u, Cer-q with the flanking genes 101kb apart, confirming they are a gene cluster, Cer-cqu. Homology-based modeling suggests that many of the mutant alleles affect overall protein structure or specific active site residues. The rich diversity of identified mutations will facilitate future studies of three key enzymes involved in synthesis of plant apoplast waxes.
authors.affiliation: Biology Department, Copenhagen University, Copenhagen DK-2200, Denmark Biology Department, Lund University, SW-22362 Lund, Sweden.
authors.forename: Lizette M
authors.initials: LM
authors.lastname: Schneider
authors.affiliation: John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK.
authors.forename: Nikolai M
authors.initials: NM
authors.lastname: Adamski
authors.affiliation: Biology Department, Copenhagen University, Copenhagen DK-2200, Denmark.
authors.forename: Caspar Elo
authors.initials: CE
authors.lastname: Christensen
authors.affiliation: Biology Department, Lund University, SW-22362 Lund, Sweden.
authors.forename: David B
authors.initials: DB
authors.lastname: Stuart
authors.affiliation: INRA-Centre National de Ressources Génomiques Végétales, F-31326 Castanet Tolosan, France.
authors.forename: Sonia
authors.initials: S
authors.lastname: Vautrin
authors.affiliation: Biology Department, Lund University, SW-22362 Lund, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Hansson
authors.affiliation: John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK.
authors.forename: Cristobal
authors.identifier: 0000-0002-9814-1770
authors.initials: C
authors.lastname: Uauy
authors.affiliation: Biology Department, Copenhagen University, Copenhagen DK-2200, Denmark knowles@bio.ku.dk.
authors.forename: Penny
authors.initials: P
authors.lastname: von Wettstein-Knowles
keywords: Barley; Cer-cqu gene cluster; Hordeum vulgare; carboxylesterase; cytochrome P450; diketone synthase (DKS); epicuticular wax; esterified alkan-2-ols; hydroxy-β-diketones; lipase; plant apoplast; type III polyketide synthase (PKS).; β-diketone aliphatics