## 2 Results and Discussion
### Varietal Effect on the Concentrations of GLVs in Grape Berries by Multivariate Analysis
Table S2 exhibits the \(p\)-values and F-values obtained by the ANOVA for the three corresponding factors (varieties, maturity and vintage) and their synergy effects. The concentrations of various volatile compounds in grapes from all sampling dates in two vintages were used as variables. The result confirmed that the GLVs concentrations varied significantly with varieties except (\(Z\))-3-hexenyl acetate, showing highly variety-dependent. A previous research stated that (\(Z\))-3-hexen-1-ol and hexanol were principal components distinguishing different varietal young red wines and their concentrations strongly relied on the variety of grape [19]. Vintage also showed the effect on most of GLVs studied, whereas maturity significantly affected the concentration of C6 aldehydes but not (\(Z\))-3-hexen-1-ol and hexyl acetate (Table S2). In addition, both variety and vintage synergistically greatly influenced hexanal, (\(E\))-2-hexenal, hexanol, and (\(E\))-2-hexen-1-ol, and the interaction of variety and maturity mainly produced effect on C6 alcohols. These results further demonstrated the formers' findings that both vintage and maturity have noticeable influence on wine grape volatiles [4; 28; 34; 35]. Comparison of Expression of Lipoxygenase-Hydroperoxides lyase (LOX-HPL) Pathway Genes in Different Grape Varieties during Berry Development  
C6 volatile compounds are direct products from the LOX-HPL pathway with LOX, HPL, ADH and alcohol acyl transferases (AAT) involved as key enzymes [36]. Figure 4 displays the expression level of major genes involved in GLVs accumulation. Detailed data are displayed in Table S3. Similar expression patterns during grape developing stages among four cultivars with nuances can be observed in these genes (Figure 4). _VvLOXA_ and _VvLOX_ are two identified 13-_VvLOXs_ in grape berries feasibly responsible for the production of C6 volatiles, and _VvLOXA_ was highly expressed in grape skins [8]. The transcript accumulation of _VvLOXA_ roughly peaked around veraison and then decreased in Chardonnay and Muscat Tchervine. This result was different from previous observation in which _VvLOXA_ expression of Sauvignon Blanc started rising after 50 DAF and remained at a relative higher  
Figure 3: Concentrations of C6 aldehydes, alcohols and esters in four varieties. Different letters among varieties mean significant differences according to Duncan test (\(p<0.05\)). level after veraison [8]. Despite so, the increasing pattern of _VvLOXA_ transcript at pre-veraison was observed in both vintages, suggesting that veraison should be a critical point for the expression of _VvLOXA_ in grape berry regardless of varieties. HPL1 catalyzes the formation of C6 aldehydes [9]. In this study, _VvHDL1_ expressed increasingly during the grape developing process especially in 2010 vintage. The transcript of _VvADH2_ was the most abundant among all _VvADHs_. The expression of _VvADH2_ presented a gradual increasing trend in developing Chardonnay grapes, which was in accordance with a previous study [37]. However, this gene expression pattern in Chardonnay grapes was totally different from those in other three  
Figure 4: Relative expression level of key genes in LOX-HPL pathway responsible for GLVs synthesis. studied varieties where this gene expression peaked around veraison and decreased in the following developmental stage. Alcohol acyl transferases (AAT) are able to convert alcohols into volatile esters. In this study a great variance among varieties was observed for _VvAAT_ transcript accumulation. The expression abundance of _VvAAT_ in Muscat Tchervine and Syrah was the highest, but this gene was expressed at very low level in Gewurztraminer throughout the developing stages. The abundant transcript of _VvAAT_ was paralleled with the high concentration of C6 esters in Muscat Tchervine berries, accordingly suggesting that a closely positive correlation existed between _VvAAT_ expression and C6 ester accumulation in developing Muscat Tchervine berries.