title: Transgenic apple plants overexpressing the chalcone 3-hydroxylase gene of Cosmos sulphureus show increased levels of 3-hydroxyphloridzin and reduced susceptibility to apple scab and fire blight.
abstract: Overexpression of chalcone-3-hydroxylase provokes increased accumulation of 3-hydroxyphloridzin in Malus . Decreased flavonoid concentrations but unchanged flavonoid class composition were observed. The increased 3-hydroxyphlorizin contents correlate well with reduced susceptibility to fire blight and scab. The involvement of dihydrochalcones in the apple defence mechanism against pathogens is discussed but unknown biosynthetic steps in their formation hamper studies on their physiological relevance. The formation of 3-hydroxyphloretin is one of the gaps in the pathway. Polyphenol oxidases and cytochrome P450 dependent enzymes could be involved. Hydroxylation of phloretin in position 3 has high similarity to the B-ring hydroxylation of flavonoids catalysed by the well-known flavonoid 3'-hydroxylase (F3'H). Using recombinant F3'H and chalcone 3-hydroxylase (CH3H) from Cosmos sulphureus we show that F3'H and CH3H accept phloretin to some extent but higher conversion rates are obtained with CH3H. To test whether CH3H catalyzes the hydroxylation of dihydrochalcones in planta and if this could be of physiological relevance, we created transgenic apple trees harbouring CH3H from C. sulphureus. The three transgenic lines obtained showed lower polyphenol concentrations but no shift between the main polyphenol classes dihydrochalcones, flavonols, hydroxycinnamic acids and flavan 3-ols. Increase of 3-hydroxyphloridzin within the dihydrochalcones and of epicatechin/catechin within soluble flavan 3-ols were observed. Decreased activity of dihydroflavonol 4-reductase and chalcone synthase/chalcone isomerase could partially explain the lower polyphenol concentrations. In comparison to the parent line, the transgenic CH3H-lines showed a lower disease susceptibility to fire blight and apple scab that correlated with the increased 3-hydroxyphlorizin contents.
authors.affiliation: Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060, Vienna, Austria.
authors.forename: Olly Sanny
authors.initials: OS
authors.lastname: Hutabarat
authors.affiliation: Federal Research Centre for Cultivated Plants, Institute of Breeding Research on Horticultural and Fruit Crops, Julius Kühn-Institut, Pillnitzer Platz 3a, 01326, Dresden, Germany.
authors.forename: Henryk
authors.initials: H
authors.lastname: Flachowsky
authors.affiliation: Unit of Fruit Science, Technical University of Munich, Dürnast 2, 85350, Freising, Germany.
authors.forename: Ionela
authors.initials: I
authors.lastname: Regos
authors.affiliation: Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060, Vienna, Austria.
authors.forename: Silvija
authors.initials: S
authors.lastname: Miosic
authors.affiliation: Chair of Urban Water Systems Engineering, Technical University of Munich, Am Coulombwall, 85748, Garching, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Kaufmann
authors.affiliation: Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060, Vienna, Austria.
authors.forename: Shadab
authors.initials: S
authors.lastname: Faramarzi
authors.affiliation: Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060, Vienna, Austria.
authors.forename: Mohammed Zobayer
authors.initials: MZ
authors.lastname: Alam
authors.affiliation: Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060, Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Gosch
authors.affiliation: Federal Research Centre for Cultivated Plants, Institute of Breeding Research on Horticultural and Fruit Crops, Julius Kühn-Institut, Pillnitzer Platz 3a, 01326, Dresden, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Peil
authors.affiliation: Federal Research Centre for Cultivated Plants, Institute for Resistance Research and Stress Tolerance, Julius Kühn-Institut, Erwin-Baur-Str. 27, 06484, Quedlinburg, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Richter
authors.affiliation: Federal Research Centre for Cultivated Plants, Institute of Breeding Research on Horticultural and Fruit Crops, Julius Kühn-Institut, Pillnitzer Platz 3a, 01326, Dresden, Germany.
authors.forename: Magda-Viola
authors.initials: MV
authors.lastname: Hanke
authors.affiliation: Unit of Fruit Science, Technical University of Munich, Dürnast 2, 85350, Freising, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Treutter
authors.affiliation: Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060, Vienna, Austria.
authors.forename: Karl
authors.initials: K
authors.lastname: Stich
authors.affiliation: Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060, Vienna, Austria. hhalb@mail.zserv.tuwien.ac.at.
authors.forename: Heidi
authors.initials: H
authors.lastname: Halbwirth
mesh_terms: D001203:Ascomycota / Q000472:pathogenicity; D019659:Asteraceae / Q000235:genetics*; D004198:Disease Susceptibility; D044084:Erwinia amylovora / Q000472:pathogenicity; D018506:Gene Expression Regulation, Plant; D027845:Malus / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology*; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D010693:Phloretin / Q000031:analogs & derivatives* / Q000378:metabolism; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D059808:Polyphenols / Q000235:genetics / Q000378:metabolism
chemical_list: C521865:3-hydroxyphloretin; D010940:Plant Proteins; D059808:Polyphenols; D006899:Mixed Function Oxygenases; D010693:Phloretin
keywords: 3-Hydroxyphloretin; 3-Hydroxyphloridzin; Chalcone 3-hydroxylase (CH3H); Dihydrochalcones; Erwinia amylovora; Malus × domestica; Venturia inaequalis