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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

Affiliation
Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060 Vienna, Austria
Hutabarat, Olly Sanny;
GND
128593652
Affiliation
Julius Kühn-Institute (JKI), Institute of Breeding Research on Horticultural and Fruit Crops, Germany
Flachowsky, Henryk;
Affiliation
Unit of Fruit Science, Technical University of Munich, Dürnast 2, 85350 Freising, Germany
Regos, Ionela;
Affiliation
Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060 Vienna, Austria
Miosic, Silvija;
Affiliation
Chair of Urban Water Systems Engineering, Technical University of Munich, Am Coulombwall, 85748 Garching, Germany
Kaufmann, Christine;
Affiliation
Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060 Vienna, Austria
Faramarzi, Shadab;
Affiliation
Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060 Vienna, Austria
Alam, Mohammed Zobayer;
Affiliation
Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060 Vienna, Austria
Gosch, Christian;
GND
172861896
Affiliation
Julius Kühn-Institute (JKI), Institute of Breeding Research on Horticultural and Fruit Crops, Germany
Peil, Andreas;
GND
1059141744
Affiliation
Julius Kühn-Institute (JKI), Institute for Resistance Research and Stress Tolerance, Germany
Richter, Klaus;
GND
1059103400
Affiliation
Julius Kühn-Institute (JKI), Institute of Breeding Research on Horticultural and Fruit Crops, Germany
Hanke, Magda-Viola;
Affiliation
Unit of Fruit Science, Technical University of Munich, Du¨rnast 2, 85350 Freising, Germany
Treutter, Dieter;
Affiliation
Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060 Vienna, Austria
Stich, Karl;
Affiliation
Institute of Chemical Engineering, Technical University of Vienna, Getreidemarkt 9, 1060 Vienna, Austria
Halbwirth, Heidi

Main conclusion 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 30 -hydroxylase (F30 H). Using recombinant F30 H and chalcone 3-hydroxylase (CH3H) from Cosmos sulphureus we show that F30 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.

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