## 3 Results
### Rootstocks Effects on Volatile-Related Gene Expression  
As a result of the observed rootstocks impacted in terms of volatile contents in grapes and wines, we analyzed the expression of the genes in aroma synthesis pathways by qRT-PCR. We selected five genes in the LOX pathway encoding the following enzymes: lipoxygenase (_VvLoXA_), alcohol dehydrogenase 1 (_VvADHI_), alcohol dehydrogenase 2 (_VvADH_2), and alcohol dehydrogenase 3 (_VvADH_3) (Figure 1B). The _VvLoXA_, _VvADHI_, _VvADH_2, and _VvADH_3 expression levels of MT-1103P were significantly down-regulated, whereas these were markedly upregulated in MN-1103P. Meanwhile, rootstock 5 BB significantly increased the expression of _VvLoXA_ in both Merlot and Marselan grapes, while _VvADH_1 and _VvADH_2 were significantly down-regulated. Rootstock SO4 limited the expression of _VvADHI_, _VvADH_2, and _VvADH_3 in Merlot grapes. We selected eight genes in the MEP pathway encoding the following enzymes: 1-deoxy-D-xylulose-5-phosphate synthase (_VvDXS1_), 1-deoxy-D-xylulose-5-phosphate synthase (_VvDXS3_), 1-deoxy-D-xylulose 5-phosphate reductase isomerase (_VvDXR_), 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (_VvHDR_) (Figure 1A), solanesyl diphosphate synthase 3 (_VvGPPS_), farnesyl diphosphate synthase (_VvFPPS_), (_3S_)-linalod/(_E_)-nerolidol synthase (_VvLinNer1_), and (_3S_)-linalod/(_E_)-nerolidol synthase (_VvLinNer2_) (Figure 1C). Compared with the levels in own-rooted samples, _VvDXS1_, _VvDXS3_, _VvDXR_, _VvHDR_, _VvFPPS_, and _VvLinNer2_ expression levels in MT-1103P were decreased observably. Contrarily, the gene expression of the MEP pathway from Marselan was significantly upregulated. 5 BB had similar effects to rootstock 1103P in Merlot in that _VvDXS3_, _VvDXR_, _VvHDR_, _VvFPPS_, _VvLinNer1_, and _VvLinNer2_ were down-regulated, while _VvDXS1_ and _VvGPPS_ showed no obvious changes. Rootstock SO4 limited the expression of all genes of the MEP pathway except for _VvGPPS_ in Merlot grapes. However, in Marselan scion-rootstocks, the _VvDXS1_, _VvHDR_, and _VvLinNer1_ expression levels were upregulated, while _VvDXS3_, _VvDXR_, _VvFPPS_, and _VvLinNer2_ had no difference compared to the levels in own-rooted samples. Especially, the gene expression of _VvGPPS_ was decreased in MN-5 BB. We selected three genes in the C13-compound synthesis pathway encoding the following enzymes: carotenoid cleavage dioxygenase 1 (_VvCCD1_), carotenoid cleavage dioxygenase 4a (_VvCCD4a_), and carotenoid cleavage dioxygenase 4b (_VvCCD4b_) (Figure 1D). Rootstocks 5 BB, 1103P, and SO4 significantly decreased the expression levels of _VvCCD1_, _VvCCD4a_, and _VvCCD4b_ in Merlot. 1103P upregulated the expression levels of _VvCCCDs_ in Marselan, whereas 5 BB upregulated the expression levels of _VvCCD4a_ and _VvCCD4b_ down-regulated that of _VvCCD1_. We selected five genes of glycosylated volatile compounds encoding the following enzymes: anthocyanin 3-O-glucosyltransferase(_VvGTS_), UDP-sugar flavonoid glycostransferase (_VvGT6_), UDP-glycostransferase (_VvGT7_), beta-D-glucosyltransferase(_VvGT9_), and 7-deoxyloganetin glucosyltransferase(_VvGT14_) (Figure 1E). Different rootstocks had different effects on Merlot GT gene expression: rootstock 5 BB down-regulated _VvGT6_ and _VvGT14_; rootstock 1103P upregulated _VvGT7_ and _VvGT9_ and down-regulated _VvGT6_ and _VvGT 14_; and rootstock SO4 down-regulated _VvGT5_, _VvGT6_, and _VvGT14_ and upregulated _VvGT7_. Except for _VvGT6_, the gene expression levels of all other _VvGTs_, including _VvGT5_, _VvGT7_, _VvGT9_, and _VvGT14_, were upregulated in Marselan-grafted 5 BB, while 1103P upregulated the expression levels of all _VvGTs_ in Marselan. On the whole, rootstocks down-regulated the expression of aroma-related genes in Merlot grapes and SO4 was the most significant, followed by 5 BB and 1103P. On the contrary, rootstocks upregulated the expression of aroma-related genes in Marselan grapes, and 1103P was better than 5 BB. Figure 1: Change in the expression of the volatile-relative genes of Merlot and Marselan.