Tree Genetics and Molecular Breeding 2025, Vol.15, No.2, 62-69 http://genbreedpublisher.com/index.php/tgmb 66 Figure 2 The relative expression level of the VvGH9 gene and the sugar content of ‘Muscat Hamburg’ grape fruit at five different developmental stages (Adopted from Xu et al., 2021) Image caption: (a) Fruit growth status in different developmental stages. Scale bars, 2 cm. (b) Relative VvGH expression in different berry developmental stages. (c) Sugar content determination results of grape berries. FS: fruit set; T: touching; V: véraison; M: mid-ripening; R: ripe. FW: fresh weight. The letters above the bars indicated the significant differences by student’s t-test (P<0.05). Three biological replicates were analyzed, and the error bars represented the SD (Adopted from Xu et al., 2021) 5.3 Implications of findings for grapevine breeding programs If breeders can clearly understand the role of the VvGH9 gene in sugar accumulation, they can design more effective breeding strategies. The fact that VvGH9 can help fruits accumulate sugar under conditions of low sugar content makes it a very worthy target for genetic manipulation. Lecourieux et al. (2014) and Xu et al. (2021) both hold that breeding projects can prioritize the selection of plants with stronger expression of VvGH9 or enhance the function of this gene through genetic engineering methods to cultivate new varieties with higher sugar content, larger fruits, and better quality. Recent studies by Zinelabidine et al. (2021) have shown that if the dominant alleles at different gene loci are used in combination with VvGH9, the additive effect between them may significantly enhance both the yield and quality of the fruit. This joint strategy may be helpful in breeding more high-quality grape varieties that meet the yield requirements of growers and the taste expectations of consumers. 6 Future Directions in Grapevine Research 6.1 Emerging gene editing techniques (CRISPR-Cas9) If the appropriate promoter can be found to enhance the expression of sgRNA and Cas9, the success rate of gene editing can be improved. Ren et al. (2021) found that this method has been used to edit genes related to sugar accumulation, such as the tonoplastic monosaccharide transporter (TMT) family, and the results show that it has great prospects in regulating fruit quality. Malnoy et al. (2016) and Najafi et al. (2022) demonstrated that the gene editing method without exogenous DNA is achieved through the CRISPR/Cas9 ribonucleoprotein complex, which can avoid the regulatory issues of transgenic organisms and is also beneficial for the development of edited plants without foreign genes. Osakabe et al. (2018) and Zhou et al. (2020) both hold that CRISPR-Cas9 can improve the fruit quality of grapevines and enhance other agronomic traits such as disease resistance. 6.2 Prospects of high-throughput genomic selection High-throughput genomic selection (HTGS) can quickly identify genes with ideal traits and conduct screening. Wan et al. (2021) believed that the combination of whole-genome sequencing data and CRISPR-Cas9 technology
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