A genomics approach reveals that aroma production in apple is controlled by ethylene predominantly at the final step in each biosynthetic pathway.
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.
Schaffer
Robert J
RJ
Horticulture and Food Research Institute of New Zealand, Mt. Albert, Auckland, New Zealand.
Friel
Ellen N
EN
Souleyre
Edwige J F
EJ
Bolitho
Karen
K
Thodey
Kate
K
Ledger
Susan
S
Bowen
Judith H
JH
Ma
Jun-Hong
JH
Nain
Bhawana
B
Cohen
Daniel
D
Gleave
Andrew P
AP
Crowhurst
Ross N
RN
Janssen
Bart J
BJ
Yao
Jia-Long
JL
Newcomb
Richard D
RD
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
D005030:Ethylenes; C036216:ethylene; D000594:Amino Acid Oxidoreductases; C059460:1-aminocyclopropane-1-carboxylic acid oxidase