Tree Genetics and Molecular Breeding 2025, Vol.15, No.2, 62-69 http://genbreedpublisher.com/index.php/tgmb 63 roles through functional research, deeply analyzed the formation mechanisms of these important traits, and understood the regulatory networks behind them. 2 Genetic Basis of Fruit Size in Grapevine 2.1 Key genes involved in fruit size regulation The VvMYB transcription factor family plays a significant role in the two key links that determine fruit size, namely cell division and cell expansion. Bogs et al. (2007) found that VvMYBPA1 could regulate the expression of genes related to proanthocyanidin synthesis in the early stage of berry development, affecting the growth and expansion of cells as well as the size of the fruit. Rossmann et al. (2020) hold that VvMYB5b is involved in the synthetic regulation of anthocyanins and proanthocyanidins, and has an impact on the overall development process of fruits and the size of fruits. Cell wall-modification enzymes such as xyloglucan endotransglucosylase/hydrolases (XTHs) and expansins (EXPs) are helpful for loosening the cell wall and promoting cell expansion. There are not many specific studies on VvXTH and VvEXP in grapevines, but studies on other plants have proved that these genes have a significant impact on regulating the structure of cell walls and the size of fruits. Bogs et al. (2007) and Rossmann et al. (2020) indicated that there might also be interactions between these enzymes and transcription factors such as VvMYB, which is beneficial for understanding their specific roles in grape fruit development. 2.2 Molecular pathways influencing fruit size VvHB58 is a homologous box transcription factor. The study by Li et al. (2019) indicated that it regulates fruit size and seed quantity through multiple hormone signaling pathways such as auxin, gibberellin, and ethylene. This gene shows different expression levels at the seed development stage of seeded and seedless grape varieties, indicating that the formation of fruit size involves complex regulatory relationships among multiple hormones. Transcription factors such as VvMYB and VvWRKY22 have regulatory effects in fruit development. Huang et al. (2021) hold that sugar is an essential energy source and material for cell growth. VvWRKY22 affects the expression of genes related to sugar, participates in sugar metabolism, and influences the size of fruits. VvMYBPA1 and VvMYB5b affect cell division and expansion as well as fruit development by regulating flavonoid related genes (Bogs et al., 2007; Deluc et al., 2008). 2.3 Recent advances in genomic studies on fruit size Genomic research has identified many important genes related to fruit size and their regulatory networks. Rossmann et al.’s research in 2020 found that the binding site of miR396 in the gene VvGRF4 had mutated, which would affect the inflorescence structure and fruit size. The fruit size of grapevines can be improved by modifying these specific genes. 2.4 Analysis of a key gene impacting fruit size in grapevine The gene VvHB58 has a regulatory effect in grapes. In tomatoes, when it is transferred into the plant body for expression, it will make the fruit smaller and the seeds fewer, indicating that its role in the development of fruit size is very prominent. Li et al. (2019) argued that its differential expression in seeded and seedless varieties indicates that it is a key gene regulating fruit size and works together through multiple hormonal pathways. 3 Genetic Basis of Sugar Content in Grapevine 3.1 Key genes involved in sugar accumulation VvSWEET10 is expressed in large quantities at the early stage of fruit ripening and can transport hexose sugars such as glucose and fructose. The research of Zhang et al. (2019) found that when its expression increased, the sugar content in grapevines also rose significantly. Ren et al. (2020) demonstrated that VvSWEET15 can promote the transport and hydrolysis of sugar, which is related to the higher hexose content in fruits. The expression of gene VvSUC11 is enhanced when encountering water stress such as severe drought, indicating that it is useful for regulating sugar distribution under adverse environmental conditions (Medici et al., 2014).
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