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
Language: English
Authors: Hutabarat, Olly Sanny 
Flachowsky, Henryk 
Regos, Ionela 
Miosic, Silvija 
Kaufmann, Christine 
Faramarzi, Shadab 
Alam, Mohammed Zobayer 
Gosch, Christian 
Peil, Andreas 
Richter, Klaus 
Hanke, Magda-Viola 
Treutter, Dieter 
Stich, Karl
Category: Research Article
Keywords: Chalcone 3-hydroxylase (CH3H); Dihydrochalcones; Erwinia amylovora; 3-Hydroxyphloretin; 3-Hydroxyphloridzin; Malus × domestica; Venturia inaequalis
Issue Date: 2016
Journal: Planta
Main conclusion

Overexpression of chalcone-3-hydroxylase provokes increased accumulation of 3-hydroxyphloridzin inMalus. 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.
DOI: 10.1007/s00425-016-2475-9
Library ID: AC11361252
URN: urn:nbn:at:at-ubtuw:3-2906
ISSN: 1432-2048
Organisation: E166 - Inst. f. Verfahrenstechnik, Umwelttechnik und Techn. Biowissenschaften 
Publication Type: Article
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