## 4 Discussion  
In grape aroma research, more than 2000 volatile components have been identified [19], and many studies have focused on the classification of aroma in different grapes. Terpenes, including sesquiterpenes and monoterpenes, are usually the main ingredient in muscul-scented cultivars; for instance, during the development of muscat-scented cultivars, linalool, and geraniol are the most important contributors to the aroma [13; 20; 21; 22]. Recent research on the muscat grape cultivars \"Shine Muscat\", \"Midnight Beauty\", and \"Centennial Seedless\" showed that the contents of linalool, geraniol, geranic acid, and terpen were higher than for other grape cultivars [23]. In our study, terpeno were also enriched the most in the muscat cultivar, \"Adenauer Rose\", and linalool (KMW0291) was the highest aromatic substance, followed by 2,7,7-trimethyl- 3-Oxatricyclo [4.1.1.0(2,4)] octane (D197), fenchone (NMW0034), and geraniol (KMW0460) (Table S3). It was interesting that in the \"Mei Xiangbao\" grape cultivar, fenchone was the terpenoid with the highest content. Based on the KEGG enrichment analysis of \"Adenauer Rose\" and \"Kyoho\" at the maturation stage, 2,7,7-trimethyl- 3-Oxatricyclo [4.1.1.0(2,4)] octane (D197) was the most enriched aromatic substance in \"Adenauer Rose\". Esters including ethyl acetate, ethyl butyrate, ethyl 2-butenoate, and ethyl 2-hexenoate are the main ingredients in strawberry-scented cultivars [12; 24]. In our study, the esters in \"Kyoho\" were less enriched than in the other two cultivars. At the maturation stage, \(\alpha\)-Terpineol (NMW0071), butanoic acid-ethyl ester (KMW0074), and benzeneacetic acid-ethyl ester (KMW0441) were the three highest aromatic substances in \"Kyoho\", while \(\alpha\)-Terpineol was down-regulated from the turning stage to the maturation stage and butanoic acid-ethyl ester and benzeneacetic acid-ethyl ester were up-regulated. Esters and terpeno were the  
Figure 7: Correlation coefficients analysis for candidate genes and aromatic substances. (**a**) Transcription factor discovery and qRT-PCR verification. Green bars represent grape turning stage and red bars represent grape maturation stage. Error bars represent the SD of three biological replicates. (**b**) Pearson correlation coefficient analysis. aromatic substances with the highest content in the \"Mei Xiangbao\" cultivar. Differing from \"Adenauer Rose\" and \"Kyooo\", the ketone (methyl 2,2,3-trimethylcyclopentyl) (XMW1442) content in \"Mei Xiangbao\" was the highest, and it was also up-regulated from the turning stage to the maturation stage. Amino acids and their biosynthetic intermediates play key roles as precursors for the biosynthesis of plant volatiles [25]. For instance, phenylalanine biosynthesis and metabolism pathways have been demonstrated to relate to plants' volatile diversity [26; 27; 28; 29]. In our study, the two candidate genes _VvASP3_(VIT_04s0008g03770) and _VvASP1_(VIT_08s0058g01000), which are involved in phenylalanine biosynthesis and the metabolism pathway, were first discovered based on the KEGG enrichment analysis. The Pearson correlation coefficients showed that these two structural genes were positively related to the content of \(\alpha\)-Pinene (KMW0148), which is a terpenoid. Moreover, we also discovered a further four structural genes also belonging to amino acid metabolism pathways; until now, no studies have reported their role in grape berry aroma formation, and the function of these three genes still needs further investigation. Ethylene response factors (ERFs), which belong to the AP2 family, play crucial roles in plant development and in the response to environmental stress. They can bind to the cis-acting element of the target gene promoter and promote the expression of ethylene-responsive genes [30; 31; 32; 33; 34]. Until now, little was known about ERFs' role in fruit aroma biosynthesis.