## 3 Results  
### IBMP Synthesis and Accumulation in Grape Berry  
The IBMP concentration in grape berries (Figure 1) and the relative expression level of _VvOMT1_, _VvOMT2_, _VvOMT3_, and _VvOMT4_ in berry skins (Figure 2) were monitored during the experimental period in 2020 and 2021.  
Firstly, the IBMP accumulation pattern in grape berries after being incorporated with deionized water (control) was almost the same as the natural condition (Mock) during the whole experiment period no matter if it was calculated in nanograms per kilogram or picograms per berry in two consecutive years. These results showed that the soaking incorporation treatment did not significantly affect IBMP accumulation in grape berries.  
The IBMP concentration in Control and Mock treatments showed a continuous downward trend during the experiment period over the 2 years (2020 and 2021). In 2020, the IBMP content peaked at 142.67 ng\(\cdot\)kg\({}^{-1}\) (Figure 2a) and 101.45 pg\(\cdot\)berry\({}^{-1}\) (Figure 2b) at 59 DAA.  
Figure 2: IBMP accumulation pattern in Cabernet Sauvignon grape berries over 2-year experimental period: (**a**) calculated in ng\(\cdot\)kg\({}^{-1}\) and (**b**) pg\(\cdot\)berry\({}^{-1}\) in the 2020 season. (**c**) IBMP content was calculated in ng\(\cdot\)kg\({}^{-1}\) and (**d**) pg\(\cdot\)berry\({}^{-1}\) in the 2021 season. BW, berry weight; DAA, days after anthesis. Data expressed as the average of three replicates \(\pm\) standard error (SE).  
In 2021, the maximum concentration of IBMP occurred at 63 DAA at 167.04 ng\(\cdot\)kg\({}^{-1}\) (Figure 2c) and 98.6 pg\(\cdot\)berry\({}^{-1}\) (Figure 2d).  
Secondly, the relative expression level of _VvOMT1_, _VvOMT2_, _VvOMT3_, and _VvOMT4_ in grape berry skins between Control and Mock treatments had no significant difference at each sample time points during the experiment period over the two years further showed that the soaking incorporation treatment did not significantly affect IBMP biosynthesis in grape berry skins.  
The relative expression level of _VvOMT1_ peaked at 59 DAA in 2020 (Figure 3a) and 63 DAA in 2021 (Figure 3b), thereinto, it showed an increased trend at pre-veraison in 2020 (Figure 3a), and then declined quickly until harvest in two years (Figure 3). This trend was synchronized with IBMP accumulation in grapes.  
Figure 3: The relative expression level of VvOMTs in Cabernet Sauvignon berry skins during the experimental period: (**a**) _VvOMT1_, (**c**) _VvOMT2_, (**e**) _VvOMT3_, and (**g**) _VvOMT4_ in the 2020 season, and (**b**) _VvOMT1_, (**d**) _VvOMT2_, (**f**) _VvOMT3_, and (**h**) _VvOMT4_ in the 2021 season.  
The relative expression level of _VvOMT2_ showed a fluctuating trend during the experiment period over the 2 years. In 2020, it was low at the early stage of the experiment, but spiked at 104 DAA and then declined rapidly at 121 DAA, increased at 128 DAA and then declined again until harvest (Figure 3c). In 2021, it was slightly increased at pre-veraison and then declined, but spiked at 101 DAA and then declined sharply at 118 DAA (Figure 3d). This trend did not show positive correlation with IBMP accumulation in grape (Figure 3c,d).  
The relative expression level of _VvOMT3_ showed the same trend during the experiment period over the 2 years. It peaked at 59 DAA in 2020 (Figure 3e) and 63 DAA in 2021 (Figure 3f), respectively, and fell sharply at veraison, and then continued to decline quickly until harvest, which was synchronous with IBMP accumulation in grape regardless of how the IBMP concentration was expressed.  
The _VvOMT4_ expression showed some difference between the 2 years. In 2020, it peaked at 59 DAA and then declined fluctuant until harvest (Figure 3g). In 2021, it showed a slight decline at pre-veraison, but increased after veraison, especially spiked at 93 DAA, and then declined sharply until harvest (Figure 3h). Therefore, the relative expression level of _VvOMT4_ may have has less relation with IBMP accumulation in grape.