## 2 Results and Discussion
### Expression of Genes Related to Volatile Compounds Formation  
Transcriptome analyses of genes that are related to aroma production in _S. cerevisiae_ have proven, to some extent, to be correlated with aroma compounds production during wine [21; 30; 31]. Given this, we have compared the relative expression levels of nineteen genes that are involved in the formation of different aroma compounds at three stages by Real-time PCR. The descriptions of these genes are listed in Table S2. The expressions of _S. cerevisiae_ genes in UFAs added wines were compared with those of the control (Figure 5). The results show that, aside quantitative variation for each gene found within the different treatments, most of them displayed the similar trend in each fermentation. UFAs addition up-regulated most genes that are involved in amino acids transportation and metabolism during fermentation. The higher expression levels of genes involved in fatty acids metabolism were observed only in 12 and 60 mg/L UFAs addition samples, with the highest values in LA_12; while the genes related to esters formation were down-regulated in most of the treatments. The formation of higher alcohols requires the activity of amino acids transporters, transaminases, decarboxylases, and dehydrogenases [30] (Figure 5). Amino acids permeases are mainly encoded by _GAP1_ and _BAP2_ genes, transaminases by _BAT1_, _BAT2_ genes, decarboxylases by _PDC1_, _PDC5_, _PDC6_, and _ARO10_, and dehydrogenases by _ADH1_[5]. The increased contents of higher alcohols in OA, LA, and ALA wines (Figure 3) were in line with the higher expressions of most aroma genes, such as _GAP1_, _BAT1_, _BAT2_, _PDC5_, and _PDC6_ comparing to the expression registered in the control. In addition, ALA_120 and ALA_240 induced higher expressions of _BAT1_, _BAT2_, _PDC1_, _PDC5_, and _PDC6_ than those of other treatments (Figure 5). This could explain how higher levels of higher alcohols were generated in ALA wines. UFAs can modulate the activity of membrane-associated enzymes and transporters to increase higher alcohols production during wine fermentation (such as amino acids permeases GAP) [6; 15; 20]. Our data were corresponding to these results, and they further indicated that the up-regulations of transaminases (_BAT1_ and _BAT2_) and decarboxylases genes (_PDC1_, _PDC5_, _PDC6_, and _ARO10_) were also involved in the enhancement of higher alcohols by UFAs addition. Medium-chain fatty acids formation entails the activity of acetyl-CoA carboxylase and the fatty acid synthase (encoded by _ACC1_, _FAS1_, and _FAS2_). _ACC1_ and _FAS1_, which are involved in the synthesis of medium-chain fatty acyl-CoA (MCFA-CoA), and their up-regulations, are usually accompanied with the high production of MCFAs [32]. _FAT3_ encodes protein required for fatty acids uptake and _ELO1_ involved in the elongation of fatty acids. Previous literatures demonstrated that exogenous UFAs could result in decreased production of FAs and UFAs in yeast by down-regulating _ACC1_, _FAS1_, and _FAS2_, and lead to low contents of MCFAs in wine [9; 15; 33]. In this study, we found that low concentrations of OA, LA, or ALA (12 and 60 mg/L) increased the expressions of _FAT3_, _ACC1_, _FAS1_, _FAS2_, and _ELO1_, and consequently resulted in high productions of MCFAs (Figure 3, Figure 5). It should be noticed that among these treatments, LA_12 and OA_60 additions presented higher expression profiles of _FAT3_, _ACC1_, _FAS1_, and _FAS2_ during fermentation. However, MCFAs contents in both wines were largely different. LA_12 wine had the highest amounts of MCFAs (including total, octanoic acid, and decanoic acid), which were 101.4%, 69.1%, and 79.9% higher than those of OA_60 wine, respectively. This implied that there might be other functional genes involved in MCFAs formations under this condition.