title: Manipulation of flavour and aroma compound sequestration and release using a glycosyltransferase with specificity for terpene alcohols.
abstract: Glycosides are an important potential source of aroma and flavour compounds for release as volatiles in flowers and fruit. The production of glycosides is catalysed by UDP-glycosyltransferases (UGTs) that mediate the transfer of an activated nucleotide sugar to acceptor aglycones. A screen of UGTs expressed in kiwifruit (Actinidia deliciosa) identified the gene AdGT4 which was highly expressed in floral tissues and whose expression increased during fruit ripening. Recombinant AdGT4 enzyme glycosylated a range of terpenes and primary alcohols found as glycosides in ripe kiwifruit. Two of the enzyme's preferred alcohol aglycones, hexanol and (Z)-hex-3-enol, contribute strongly to the 'grassy-green' aroma notes of ripe kiwifruit and other fruit including tomato and olive. Transient over-expression of AdGT4 in tobacco leaves showed that enzyme was able to glycosylate geraniol and octan-3-ol in planta whilst transient expression of an RNAi construct in Actinidia eriantha fruit reduced accumulation of a range of terpene glycosides. Stable over-expression of AdGT4 in transgenic petunia resulted in increased sequestration of hexanol and other alcohols in the flowers. Transgenic tomato fruit stably over-expressing AdGT4 showed changes in both the sequestration and release of a range of alcohols including 3-methylbutanol, hexanol and geraniol. Sequestration occurred at all stages of fruit ripening. Ripe fruit sequestering high levels of glycosides were identified as having a less intense, earthier aroma in a sensory trial. These results demonstrate the importance of UGTs in sequestering key volatile compounds in planta and suggest a future approach to enhancing aromas and flavours in flowers and during fruit ripening.
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited (PFR), Private Bag 92169, Auckland, 1142, New Zealand.
authors.forename: Yar-Khing
authors.initials: YK
authors.lastname: Yauk
authors.forename: Claire
authors.initials: C
authors.lastname: Ged
authors.forename: Mindy Y
authors.initials: MY
authors.lastname: Wang
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Matich
authors.forename: Lydie
authors.initials: L
authors.lastname: Tessarotto
authors.forename: Janine M
authors.initials: JM
authors.lastname: Cooney
authors.forename: Christian
authors.initials: C
authors.lastname: Chervin
authors.forename: Ross G
authors.initials: RG
authors.lastname: Atkinson
mesh_terms: D029042:Actinidia / Q000201:enzymology* / Q000378:metabolism; D000438:Alcohols / Q000378:metabolism*; D002853:Chromatography, Liquid; D016695:Glycosyltransferases / Q000378:metabolism*; D007700:Kinetics; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009812:Odorants; D030821:Plants, Genetically Modified; D013379:Substrate Specificity; D013729:Terpenes / Q000378:metabolism*
chemical_list: D000438:Alcohols; D013729:Terpenes; D016695:Glycosyltransferases
keywords: Actinidia deliciosa; aroma; flavour; fruit; glycoside; glycosyltransferase; kiwifruit; volatile