## 3 Discussion
### Potential Regulation Relating to NAA-Induced Norisoprenoid Accumulation  
GATA transcription factors are a family of zinc finger proteins that bind the consensus DNA sequence (T/A) GATA (A/G) [38]. They are widely present in plants and involved in light response regulation, chlorophyll synthesis, and carbon/nitrogen metabolism. Interestingly, Evidence has demonstrated that light is the most important environmental factors affecting plant carotenoid metabolism; light significantly promotes the expression of carotenoid biosynthetic genes, particularly PYS and the activity of the related enzymes [39]. In the present study, integrated WGCNA and DAP-seq analysis indicated that VviGATA26 played a critical role in the regulatory network relating to NAA-induced norisoprenoid biosynthesis based on the following data. Firstly, VviGATA26 was indicated to be able to bind with the promoter sequence of VviPSY1 (VIT_204s0079g00680) and VviZDS (VIT_214s0030g01740), and VviGATA26 exhibited an opposite expression pattern with the two target genes at the transcriptional level (Figure 7B). Both VviPSY and VviZDS are crucial enzymes in the biosynthesis of norisoprenoid precursor of carotenoid [40]. As the rate-limiting step of carotenogenesis, VviPSY1 has garnered much attention and numerous strategies targeting PSY1 have been performed to increase carotenoid concentration in tomato [41]. Over-expression of AtZDS in tomato resulted in the increased carotenoid all trans-lycopene, and reduced carotenoid content was found in ZDS repressed fruit [42]. Secondly, the expression of these two target genes, especially VviPSY1, was reversely paralleled with the accumulation of (E)-\(\beta\)-damascenone, (Z)-\(\beta\)-damascenone, and total norisoprenoids (Table S8). Thirdly, the higher expression of VviGATA26 expression was showed in NAA-treated berries at E-L 36 stage compared to the control (Figure 7B). Combining these three points, we hypothesized that VviGATA26 could positively respond to NAA treatment and be triggered to down-regulate the two upstream genes and resulted in the increased accumulation of norisoprenoids. In addition, VviGATA26 expression was positively correlated with VviCCD4a, VviPSY2, VviPSY3 and VviZEPs (Figure 7B), but VviGATA26 cannot bind to the promoter regions of these genes according to DAP-seq. A possible explanation is that VviGATA26 indirectly affects the expression of these genes via regulatory cascades. Two TFs VviMYB RADIALIS (VIT_207s0005g02730) and VviMADS-box (VIT_213s0158g00100) were also precited to involve in norisoprenoid accumulation based on their co-expression patterns with VviPSY3. Both MYB and MADS-box transcription factor families have been demonstrated to associate with ripening process modulation [43; 44]. Our previous study has elucidated that MADS4 (VIT_201s0010g03900) can participate in the regulation of norisoprenoid accumulation by negatively regulating VviCCD4b [12]. In citrus, a MADS transcription factor, CsMADS6 was reported to be able to bind to the promoter of PSY and up-regulated its expression [45]. However, the present data is far from supporting our hypothesis regarding the regulatory function of the VviMYB RADIALIS and VviMADS-box in norisoprenoid biosynthesis. In future work, the genome-editing techniques or transgenic grapevines will be used to verify this point. AS, as an important posttranscriptional regulation of genes, has been reported to happen in 8668 genes of v2 predicted genes (29150) in grape berry [9]. As observed in grape and Arabidopsis [11; 46], AS contribute significantly to the transcriptional complexity and should be taken into consideration when performing genome wider transcriptomic studies. The expression of the isoforms of VviDXS and VviCRTISO was significantly altered in the comparison of NAA and control, which may then affect the protein properties and finally contribute to higher norisoprenoid.