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

Main conclusionOverexpression 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.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-016-2475-9) contains supplementary material, which is available to authorized users.

Silencing a phloretin‐specific glycosyltransferase perturbs both general phenylpropanoid biosynthesis and plant development

“…This inferred that there was a threshold level of phloridzin or other downstream polyphenols required in apple for normal growth. It is unlikely that the 65–75% reduction in phloridzin levels that we observed in the UGT88F1 knockdown lines represents the exact threshold for normal development, however, as previous studies (Dare et al ., ; Hutabarat et al ., ) reported similar fold decreases in phloridzin levels relative to control plants. There were no reported changes in phenotype in these studies.…”

Metabolic engineering of Saccharomyces cerevisiae for de novo production of dihydrochalcones with known antioxidant, antidiabetic, and sweet tasting properties

“…During preparation of this manuscript another study was published, reporting the ability of CsCh3h to accept phloretin as substrate, both in yeast and in plants. Overexpression of CsCh3h in apple resulted in increased production of 3-hydroxyphlorizin, which correlated with reduced susceptibility to fire blight and scab (Hutabarat et al, 2016). …”

“…1B). During the preparation of this manuscript, a study was published, reporting that chalcone 3-hydroxylase (CH3H) from Cosmos sulphureus can hydroxylate phloretin to form 3-hydroxyphloretin in yeast and in plants (Hutabarat et al, 2016). During the revision of this manuscript, an additional study was published, reporting that MdPh-4′-OGT from Malus × domestica can glycosylate the 4′-hydroxygroup of phloretin to form trilobatin (Yahyaa et al, 2016).…”

MdUGT88F1-Mediated Phloridzin Biosynthesis Regulates Apple Development and Valsa Canker Resistance

“…Phloridzin appears to play important physiological roles in plant development and pathogen defense in apple (Zhang et al, 2007;Hutabarat et al, 2016). In this study, we used MdUGT88F1, the key P29GT gene, transgenic apple lines, and wild Malus spp.…”