title: A genomics approach reveals that aroma production in apple is controlled by ethylene predominantly at the final step in each biosynthetic pathway.
abstract: Ethylene is the major effector of ripening in many fleshy fruits. In apples (Malus x domestica) the addition of ethylene causes a climacteric burst of respiration, an increase in aroma, and softening of the flesh. We have generated a transgenic line of 'Royal Gala' apple that produces no detectable levels of ethylene using antisense ACC OXIDASE, resulting in apples with no ethylene-induced ripening attributes. In response to external ethylene these antisense fruits undergo a normal climacteric burst and produced increasing concentrations of ester, polypropanoid, and terpene volatile compounds over an 8-d period. A total of 186 candidate genes that might be involved in the production of these compounds were mined from expressed sequence tags databases and full sequence obtained. Expression patterns of 179 of these were assessed using a 15,720 oligonucleotide apple microarray. Based on sequence similarity and gene expression patterns we identified 17 candidate genes that are likely to be ethylene control points for aroma production in apple. While many of the biosynthetic steps in these pathways were represented by gene families containing two or more genes, expression patterns revealed that only a single member is typically regulated by ethylene. Only certain points within the aroma biosynthesis pathways were regulated by ethylene. Often the first step, and in all pathways the last steps, contained enzymes that were ethylene regulated. This analysis suggests that the initial and final enzymatic steps with the biosynthetic pathways are important transcriptional regulation points for aroma production in apple.
authors.affiliation: Horticulture and Food Research Institute of New Zealand, Mt. Albert, Auckland, New Zealand.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Schaffer
authors.forename: Ellen N
authors.initials: EN
authors.lastname: Friel
authors.forename: Edwige J F
authors.initials: EJ
authors.lastname: Souleyre
authors.forename: Karen
authors.initials: K
authors.lastname: Bolitho
authors.forename: Kate
authors.initials: K
authors.lastname: Thodey
authors.forename: Susan
authors.initials: S
authors.lastname: Ledger
authors.forename: Judith H
authors.initials: JH
authors.lastname: Bowen
authors.forename: Jun-Hong
authors.initials: JH
authors.lastname: Ma
authors.forename: Bhawana
authors.initials: B
authors.lastname: Nain
authors.forename: Daniel
authors.initials: D
authors.lastname: Cohen
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Gleave
authors.forename: Ross N
authors.initials: RN
authors.lastname: Crowhurst
authors.forename: Bart J
authors.initials: BJ
authors.lastname: Janssen
authors.forename: Jia-Long
authors.initials: JL
authors.lastname: Yao
authors.forename: Richard D
authors.initials: RD
authors.lastname: Newcomb
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000235:genetics / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000502:physiology*; D005030:Ethylenes / Q000378:metabolism*; D005638:Fruit / Q000378:metabolism*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D023281:Genomics; D027845:Malus / Q000235:genetics / Q000378:metabolism*; D005810:Multigene Family; D009154:Mutation; D009812:Odorants; D020411:Oligonucleotide Array Sequence Analysis; D014835:Volatilization
chemical_list: D005030:Ethylenes; C036216:ethylene; D000594:Amino Acid Oxidoreductases; C059460:1-aminocyclopropane-1-carboxylic acid oxidase