Plant Cell, doi:10.1105/tpc.113.114231

Credit: YURY TIKUNOV

Volatile organic compounds influence how humans perceive and evaluate fruit. For instance, phenylpropanoid volatiles such as guaiacol contribute to the 'smoky' aroma of certain tomato varieties. These compounds are stored as disaccharide glycoconjugates during fruit development and are released upon consumption by the action of glycosyl hydrolases. Previous work has shown that in 'non-smoky' tomatoes, these glycoconjugates are converted to trisaccharides that are resistant to hydrolysis and prevent release of smoky volatiles. Tikunov et al. now report the identification of the glycosyltransferase that controls tomato smokiness. Unbiased gene expression analysis using next-generation sequencing of tissue from a panel of smoky and non-smoky tomato cultivars identified two linked genes associated with the non-smoky phenotype, which the authors termed NON-SMOKY GLYCOSYLTRANSFERASE 1 and 2 (NSGT1 and NSGT2). Though NSGT genes were found in some smoky cultivars, they seem to be nonfunctional. Metabolic profiling reveals that expression of NSGT1 in non-smoky cultivars correlates with increased trisaccharide conjugates and reduced volatile emission. In vitro assays with expressed enzyme confirmed that NSGT1 is a glucosyltransferase that uses disaccharide-phenylpropanoid substrates. Expression of NSGT1 in a smoky line engenders a non-smoky phenotype, a property that was detected by sensory analysis of tomato aromas by a panel of experts. In addition to revealing that NSGT1 regulates smoky aroma expression in tomatoes, the study highlights a potential horticultural strategy for breeding tomatoes with desired aroma properties.