Identification and expression analysis of folate-biopterin transporter (FBT) genes in grape berry reveals candidates associated with fruit ripening

The folate-biopterin transporter (FBT) family is a vital class of membrane transport proteins involved in folate and biopterin transport. Exogenous folate applied at the early stage of fruit development was shown to accelerate grape ripening; therefore, identifying FBTs in grape and analyzing their expression is crucial for understanding the ripening mechanism. This study identified ten FBT genes. All the proteins were highly hydrophobic and predicted to localize in the cell membrane based on bioinformatic analysis. The promoters of VvFBTs contained cis-acting elements related to plant growth and development. A transcriptional regulatory network centered on the VvFBT genes was constructed, and GO enrichment analysis revealed that these genes were associated with grape growth and development. Protein interaction network analysis revealed that proteins closely associated with VvFBTs included enzymes involved in folate synthesis. The quantitative real-time PCR analyses revealed that the expression of VvFBT4, VvFBT8, and VvFBT9 peaked at veraison. Overexpression of VvFBT9 in 'Kyoho' fruit calli up-regulated the expression of ripening-related genes, indicating that VvFBT9 exerted a positive regulatory effect on fruit ripening. These results provided a theoretical basis for investigating the functions of the VvFBT genes and offered new insights into exploring their roles during fruit ripening.