NON-SMOKY GLYCOSYLTRANSFERASE1 Prevents the Release of Smoky Aroma from Tomato Fruit

Abstract

ORCID ID: 0000-0001-5417-5066 (Y.M.T.).Phenylpropanoid volatiles are responsible for the key tomato fruit (Solanum lycopersicum) aroma attribute termed "smoky." Release of these volatiles from their glycosylated precursors, rather than their biosynthesis, is the major determinant of smoky aroma in cultivated tomato. Using a combinatorial omics approach, we identified the NON-SMOKY GLYCOSYLTRANSFERASE1 (NSGT1) gene. Expression of NSGT1 is induced during fruit ripening, and the encoded enzyme converts the cleavable diglycosides of the smoky-related phenylpropanoid volatiles into noncleavable triglycosides, thereby preventing their deglycosylation and release from tomato fruit upon tissue disruption. In an nsgt1/nsgt1 background, further glycosylation of phenylpropanoid volatile diglycosides does not occur, thereby enabling their cleavage and the release of corresponding volatiles. Using reverse genetics approaches, the NSGT1-mediated glycosylation was shown to be the molecular mechanism underlying the major quantitative trait locus for smoky aroma. Sensory trials with transgenic fruits, in which the inactive nsgt1 was complemented with the functional NSGT1, showed a significant and perceivable reduction in smoky aroma. NSGT1 may be used in a precision breeding strategy toward development of tomato fruits with distinct flavor phenotypes.

Volatile Glycosylation in Tea Plants: Sequential Glycosylations for the Biosynthesis of Aroma β-Primeverosides Are Catalyzed by Two Camellia sinensis Glycosyltransferases

“…CsGT1 showed high similarity to cassava (Manihot esculenta) UGT85K4 and UGT85K5 involved in the biosynthesis of cyanogenic glucosides (Kannangara et al, 2011). In contrast, CsGT2 constitutes a new member of the so-called sugarsugar UGT or glycoside-specific glycosyltransferase (GGT) group that specifically catalyzes glycosylation at the sugar moiety of various phytochemical glycosides (but not aglycones), including the morning glory DUSKY (UGT79G16) and tomato NSGT1 involved in the glucosylation of anthocyanin and volatile glycosides, respectively (Morita et al, 2005;Tikunov et al, 2013).…”

“…This unique Ile-141 was found to be conserved in two xylosyltransferases specific for flavonoid glycosides, kiwi F3GGT1 (Ile-136) and Arabidopsis UGT79B1 (Ile-142; Montefiori et al, 2011;Yonekura-Sakakibara et al, 2012; Table II). In contrast, various amino acid residues occupy this position in other structurally similar glycosyltransferases, including morning glory (Ipomoea purpurea) UGT79G16 (Thr-138), Sesamum indicum UGT94D1 (Ser-140), Veronica persica UGT94F1 (Ala-144), and tomato NONSMOKY GLYCOSYLTRANSFERASE1 (Sl_NSGT1 ; Table II; Morita et al, 2005;Noguchi et al, 2008;Ono et al, 2010b;Tikunov et al, 2013). To assess the functional relevance of Ile-141 for the specificity toward UDP-Xyl, a CsGT2-I141S mutant was generated by sitespecific mutagenesis, in which Ile-141 was replaced by a Ser residue.…”

“…Interestingly, various sugars (i.e. Xyl, Ara, apiose, and Rha) could be attached to monoglycosides of VOCs as second sugar molecules (Tikunov et al, 2013;Bönisch et al, 2014b). This observation suggests that the second sugar moiety of the glycoconjugated VOCs further increases stability, which leads to the accumulation of such glycoconjugated VOCs.…”

“…CsGT2 belongs to the GGT cluster (OG8), with regio-specificity for the C-2 hydroxy or C-6 hydroxy group of sugar moieties of various phytochemical glycosides (Noguchi et al, 2008). CsGT2 is phylogenetically related to tomato NSGT1, which catalyzes the third 2-O-glucosylation of volatile-derived diglycosides (Tikunov et al, 2013; Fig. 7).…”

Identification and Mode of Inheritance of Quantitative Trait Loci for Secondary Metabolite Abundance in Tomato

“…Targeted QTL analyses have also been performed on volatile organic compounds, pigments, cell wall components, sesquiterpenes, and acyl-sugars in the Solanum pennellii introgression line population (Liu et al, 2003;Tieman et al, 2006;Fraser et al, 2007;Schilmiller et al, 2010;de Godoy et al, 2013). Screens of natural variance have additionally focused on a similar range of compounds (Sallaud et al, 2009;Gonzales-Vigil et al, 2012;Schilmiller et al, 2012;Matsuba et al, 2013;Tikunov et al, 2013), but also of cuticle composition (Yeats et al, 2012). In some cases, the observed considerable variation in the contents of these chemical constituents has been related to the growth habit to which the wild species of tomato have adapted (Schauer et al, 2005;Yeats et al, 2012;Ichihashi and Sinha, 2014).…”