title: Functional characterization of SlscADH1, a fruit-ripening-associated short-chain alcohol dehydrogenase of tomato.
abstract: A tomato short-chain dehydrogenase-reductase (SlscADH1) is preferentially expressed in fruit with a maximum expression at the breaker stage while expression in roots, stems, leaves and flowers is very weak. It represents a potential candidate for the formation of aroma volatiles by interconverting alcohols and aldehydes. The SlscADH1 recombinant protein produced in Escherichia coli exhibited dehydrogenase-reductase activity towards several volatile compounds present in tomato flavour with a strong preference for the NAD/NADH co-factors. The strongest activity was observed for the reduction of hexanal (K(m)=0.175mM) and phenylacetaldehyde (K(m)=0.375mM) in the presence of NADH. The oxidation process of hexanol and 1-phenylethanol was much less efficient (K(m)s of 2.9 and 23.0mM, respectively), indicating that the enzyme preferentially acts as a reductase. However activity was observed only for hexanal, phenylacetaldehyde, (E)-2-hexenal and acetaldehyde and the corresponding alcohols. No activity could be detected for other aroma volatiles important for tomato flavour, such as methyl-butanol/methyl-butanal, 5-methyl-6-hepten-2-one/5-methyl-6-hepten-2-ol, citronellal/citronellol, neral/nerol, geraniol. In order to assess the function of the SlscADH1 gene, transgenic plants have been generated using the technique of RNA interference (RNAi). Constitutive down-regulation using the 35S promoter resulted in the generation of dwarf plants, indicating that the SlscADH1 gene, although weakly expressed in vegetative tissues, had a function in regulating plant development. Fruit-specific down-regulation using the 2A11 promoter had no morphogenetic effect and did not alter the aldehyde/alcohol balance of the volatiles compounds produced by the fruit. Nevertheless, SlscADH1-inhibited fruit unexpectedly accumulated higher concentrations of C5 and C6 volatile compounds of the lipoxygenase pathway, possibly as an indirect effect of the suppression of SlscADH1 on the catabolism of phospholipids and/or integrity of membranes.
authors: Université de Toulouse, INPT-ENSAT, Génomique et Biotechnologie des Fruits, Avenue de l'Agrobiopole BP 32607, 31326 Castanet-Tolosan, France.
authors: Hanane
authors: H
authors: Moummou
authors: Libert Brice
authors: LB
authors: Tonfack
authors: Christian
authors: C
authors: Chervin
authors: Mohamed
authors: M
authors: Benichou
authors: Emmanuel
authors: E
authors: Youmbi
authors: Christian
authors: C
authors: Ginies
authors: Alain
authors: A
authors: Latché
authors: Jean-Claude
authors: JC
authors: Pech
authors: Benoît
authors: B
authors: van der Rest
mesh_terms: D000079:Acetaldehyde / Q000031:analogs & derivatives / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D000447:Aldehydes / Q000378:metabolism*; D000595:Amino Acid Sequence; D015536:Down-Regulation; D035264:Flowers / Q000201:enzymology; D005638:Fruit / Q000254:growth & development*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology; D018517:Plant Roots / Q000201:enzymology; D018547:Plant Stems / Q000201:enzymology; D055549:Volatile Organic Compounds / Q000378:metabolism
chemical_list: D000447:Aldehydes; D010743:Phospholipids; D055549:Volatile Organic Compounds; C010463:n-hexanal; D000429:Alcohol Oxidoreductases; D000079:Acetaldehyde; C013192:phenylacetaldehyde