Farnesyl diphosphate synthase may determine the accumulation level of (−)-rotundone in 'Syrah' grapes

Abstract

(−)-Rotundone is an oxygenated sesquiterpene responsible for the peppery aroma in grapes, wines, herbs, and spices, and it was first identified in 'Syrah' wine from Australia. In this study, we demonstrated the expression profiles of genes related to (−)-rotundone biosynthesis during the maturation of 'Syrah' grapes from two different vineyards, namely, the Iwaimura and Johnohira vineyards in Japan. The α-guaiene and (−)-rotundone accumulation levels in the grape exocarp from the Johnohira vineyard, which has a cool climatic condition located at a high altitude, were extremely higher than those from the Iwaimura vineyard. Among the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway genes, the transcript levels of 1-deoxy-D-xylulose-5-phosphate synthase gene (DXS) in the grape exocarp from the Johnohira vineyard were higher than those from the Iwaimura vineyard after véraison. The expression levels of the mevalonate pathway genes, Vitis vinifera terpene synthase gene (VvTPS24) and cytochrome P450 gene (CYP71BE5) in the final step of (−)-rotundone biosynthesis were not significantly different between samples from the two vineyards during grape maturation. In contrast, the farnesyl diphosphate synthase gene (FPPS) expression level was considerably higher in the grape exocarp from the Johnohira vineyard than in that from the Iwaimura vineyard. Consistent with these observations, FPPS was constantly expressed at higher level in 'Syrah' grape exocarp compared with 'Merlot' grape which is a low-rotundone cultivar. These findings suggest that FPPS may play a key role in determining the accumulation level of (−)-rotundone, which can provide abundant substrates for VvTPS24 catalysis to produce α-guaiene as a precursor of (−)-rotundone. In addition, among the MEP pathway genes, DXS may have a regulatory role for a precursor supply from the plastids to (−)-rotundone biosynthesis.