Cytochrome P450 CYP71BE5 from grapevine (Vitis vinifera) catalyzes the formation of the spicy aroma compound, (-)-rotundone

Abstract

(-)-Rotundone, an oxygenated sesquiterpene, is a potent odorant molecule with a characteristic spicy aroma existing in various plants including grapes1. It is considered as a significant compound notably in wines and grapes because of its low sensory threshold (16 ng L-1 in red wine, 8 ng L-1 in water) and aroma properties. (-)-Rotundone was first identified in red wine made from the grape cultivar Syrah (regionally called Shiraz) in Australia1, and then it was found in several grape varieties such as Duras, Grüner Veltliner, Schioppettino and Vespolina from Europe2, 3. Several environmental factors affecting the accumulation of (-)-Rotundone during the grape maturation, were reported such as ambient temperature4, soil properties and topography5, soil moisture from irrigation and light exposure in the bunch zone by leaf removal2. However, the biosynthetic pathway of (-)-rotundone in grapevine has been unclarified to date. In this study, we report the identification of VvSTO2 as a α-guaiene 2-oxidase which can transform α-guaiene to (-)-rotundone in the grape cultivar Syrah6. It is a cytochrome P450 (CYP) belonging to the CYP 71BE subfamily, which overlaps with the very large CYP71D family and, to the best of our knowledge, this is the first functional characterization of an enzyme from this family. VvSTO2 generated (-)-rotundone as the major reaction product with α-guaiene, and presumably (2R)-rotundol and (2S)-rotundol as the intermediate compounds to synthesize (-)-rotundone were found at trace levels in vitro enzyme assay. This result suggests that this enzyme can catalyze a one-step oxidation of α-guaiene to (-)-rotundone or a two-step oxidation via a rapid second oxidation from (2R)-rotundol and (2S)-rotundol to (-)-rotundone. VvSTO2 was expressed at a higher level in the Syrah grape exocarp (skin) in accord with the localization of (-)-rotundone accumulation in grape berries. α-Guaiene was also detected in the Syrah grape exocarp at an extremely high concentration. These findings suggest that (-)-rotundone accumulation is regulated by the VvSTO2 expression along with the availability of α-guaiene as a precursor. VvSTO2 expression during grape maturation was considerably higher in Syrah grape exocarp compared to Merlot grape exocarp, consistent with the patterns of α-guaiene and (-)-rotundone accumulation. On the basis of these findings, we propose that VvSTO2 may be a key enzyme in the biosynthesis of (-)-rotundone in grapevines by acting as a α-guaiene 2-oxidase. [References] [1] Wood, C., et al. 2008. J. Agric. Food Chem. 56, 3738-44. [2] Geffroy, O., et al. 2014. Aust. J. Grape Wine Res. 20, 401-408. [3] Mattivi, F., et al. 2011. Rapid Commun. Mass Spectrom. 25, 483-8. [4] Caputi, L., et al. 2011. J. Agric. Food Chem. 59, 5565-71. [5] Scarlett, N.J., et al. 2014. Aust. J. Grape Wine Res. 20, 214-222. [6] Takase, H., et al. 2015. J. Exp. Bot, in press.