Genome-wide identification of the SWEET gene family in grape (Vitis vinifera L.) and expression analysis of VvSWEET14a in response to water stress

Sugars are considered primary metabolites that determine the flavor and quality of grape berries, also playing a crucial role in the plants to resist stress. Sugars Will Eventually be Exported Transporters (SWEETs) gene family has been previously reported to be involved in the growth and development of grape, while the changes in transcriptional levels under water stress remain unclear. In this study, sixteen grape SWEETs members were identified and annotated based on their homologous genes in Arabidopsis and tomato, they were classified into four clades (Clades I to IV) with VvSWEETs by phylogenetic analysis. The highly conserved motifs and gene structures of VvSWEETs indicate that they are closely evolutionary conservation. Chromosomal localization and synteny analysis found that VvSWEETs were unevenly distributed on 11 chromosomes, and the VvSWEET5a, VvSWEET5b, VvSWEET14b and VvSWEET14c existed a relatively recent evolutionary relationship. Promoter cis-acting elements showed that the clade III has more ABRE motif, especially the VvSWEET14a. The regulation of VvSWEETs is mainly influenced by the Dof and MYB families, which are associated with grape ripening, while VvSWEET14a is closely related to the bHLH, MYB, NAC, and bZIP families. RT-qPCR data and subcellular localization show that VvSWEET14a was highly induced under early water stress and is located in the vacuole membrane. The instantaneous transformation assay identified that this gene could promote to transport hexose in the vacuole to maintain normal osmotic pressure. In summary, our study provides a basis for further research on SWEET genes function and regulatory mechanism in the future, and lays the foundation for stress resistance breeding of Vitis vinifera.