Abstract
Norisoprenoids are important aromatic volatiles contributing to the pleasant floral/fruity odor in grapes and wine. They are produced from carotenoids through the cleavage of carotenoid cleavage dioxygenases (CCDs). However, the underlying mechanisms regulating VvCCD expression remain poorly understood. In this study, we showed that VvCCD4b expression was positively correlated with the accumulation of β-damascenone, β-ionone, 6-methyl-5-hepten-2-one, geranylacetone, dihydroedulan I, and total norisoprenoids in developing grapes in two vintages from two regions. VvCCD4b was found to be principally expressed in flowers, mature leaves, and berries. Abscisic acid strongly induced the expression of this gene. Additionally, the present study preliminarily indicated that the activity of the VvCCD4b promoter was dropped under 37°C treatment and also responded to the illumination change. VvCCD4b was expressed in parallel with VvMADS4 in developing grape berries. The latter is a MADS family transcription factor and nucleus-localized protein that was captured by yeast one-hybrid. A dual-luciferase reporter assay in tobacco leaves revealed that VvMADS4 downregulated the activity of the VvCCD4b promoter. VvMADS4 overexpression in grape calli and Vitis quinquangularis Rehd. leaves repressed the VvCCD4b expression. In summary, this work demonstrates that VvCCD4b expression is positively correlated with the accumulation of norisoprenoids, and VvMADS4 is a potential negative regulator of VvCCD4b. Our results provide a new perspective for understanding the regulation of VvCCD4b expression and norisoprenoid accumulation in grapes.
Highlights
Norisoprenoids are volatile C9, C10, C11, and C13 molecules with a low odor perception threshold, generating the floral and fruity scents in grape berries and wine
VvCCD4b expression was significantly correlated with the total concentration of norisoprenoids, indicating that VvCCD4b is a key enzyme in norisoprenoid production during grape berry development
Overexpression experiments in carotenoidaccumulating E. coli or S. cerevisiae verified that VvCCD1 cleaves zeaxanthin, lycopene, ε-carotene, and β-carotene to yield 3-hydroxy-β-ionone, MHO, geranylacetone, β-ionone, and β-cyclocitral, respectively (Mathieu et al, 2005; Lashbrooke et al, 2013; Meng et al, 2019)
Summary
Norisoprenoids are volatile C9, C10, C11, and C13 molecules with a low odor perception threshold, generating the floral and fruity scents in grape berries and wine. The content of monoterpenes is extremely low in neutral grape varieties and their corresponding wines Norisoprenoids are more important than other terpenoids in forming the characteristic aromas of these varieties, because the norisoprenoid concentrations tend to be higher than their thresholds (Mateo and Jiménez, 2000). Several norisoprenoids are the Expression and Regulation of VvCCD4b primary contributors to aroma in red and white grapes and wines Aged Riesling wines have a floral profile of “kerosene” and “petrol” owing to the presence of 1,1,5-trimethyl-1,2-dihydronaphthalene (TDN) (Simpson, 1978; Simpson and Miller, 1983)
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