title: Two highly divergent alcohol dehydrogenases of melon exhibit fruit ripening-specific expression and distinct biochemical characteristics.
abstract: Alcohol dehydrogenases (ADH) participate in the biosynthetic pathway of aroma volatiles in fruit by interconverting aldehydes to alcohols and providing substrates for the formation of esters. Two highly divergent ADH genes (15% identity at the amino acid level) of Cantaloupe Charentais melon (Cucumis melo var. Cantalupensis) have been isolated. Cm-ADH1 belongs to the medium-chain zinc-binding type of ADHs and is highly similar to all ADH genes expressed in fruit isolated so far. Cm-ADH2 belongs to the short-chain type of ADHs. The two encoded proteins are enzymatically active upon expression in yeast. Cm-ADH1 has strong preference for NAPDH as a co-factor, whereas Cm-ADH2 preferentially uses NADH. Both Cm-ADH proteins are much more active as reductases with K (m)s 10-20 times lower for the conversion of aldehydes to alcohols than for the dehydrogenation of alcohols to aldehydes. They both show strong preference for aliphatic aldehydes but Cm-ADH1 is capable of reducing branched aldehydes such as 3-methylbutyraldehyde, whereas Cm-ADH2 cannot. Both Cm-ADH genes are expressed specifically in fruit and up-regulated during ripening. Gene expression as well as total ADH activity are strongly inhibited in antisense ACC oxidase melons and in melon fruit treated with the ethylene antagonist 1-methylcyclopropene (1-MCP), indicating a positive regulation by ethylene. These data suggest that each of the Cm-ADH protein plays a specific role in the regulation of aroma biosynthesis in melon fruit.
authors.affiliation: UMR 990 INRA/INPT-ENSAT "Génomique et Biotechnologie des Fruits", Av. de l'Agrobiopole, BP 32607, F-31326, Castanet-Tolosan Cedex, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Manríquez
authors.forename: Islam
authors.initials: I
authors.lastname: El-Sharkawy
authors.forename: Francisco B
authors.initials: FB
authors.lastname: Flores
authors.forename: Fikri
authors.initials: F
authors.lastname: El-Yahyaoui
authors.forename: Farid
authors.initials: F
authors.lastname: Regad
authors.forename: Mondher
authors.initials: M
authors.lastname: Bouzayen
authors.forename: Alain
authors.initials: A
authors.lastname: Latché
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Pech
mesh_terms: D000426:Alcohol Dehydrogenase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D000447:Aldehydes / Q000378:metabolism; D000595:Amino Acid Sequence; D019662:Cucurbitaceae / Q000201:enzymology* / Q000235:genetics; D005638:Fruit / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D007700:Kinetics; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010802:Phylogeny; D013379:Substrate Specificity
chemical_list: D000447:Aldehydes; D009243:NAD; D009249:NADP; D000426:Alcohol Dehydrogenase