Molecular cloning and functional analysis of a sugar transporter gene (CsTST2) from cucumber (Cucumis sativus L.)

Tonoplast sugar transporters (TSTs) usually act as antiporters to import sugars across the tonoplast and play essential roles in regulating diverse growth and developmental processes as well as in response to various abiotic stresses in plants. In this study, a putative TST gene named CsTST2 was isolated and characterized from cucumber (Cucumis sativus L.). CsTST2 possesses a 2202-bp open reading frame encoding a highly hydrophobic protein of 733 amino acids with a molecular weight (MW) of 78.30 kDa and an isoelectric point of 5.13. Multiple sequence alignment and phylogenetic analysis suggested that CsTST2 has the highest identity and closest phylogenetic relationship with CmTST2 and ClTST2. Expression analysis with transcriptome data revealed that CsTST2 has differential expression patterns in various tissues and developmental stages. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) showed that CsTST2 is responsive to various abiotic stresses, inducing salt, drought and cold. Yeast complementation assays indicated that CsTST2 can mediate the uptake of fructose, galactose, mannose and sucrose. These findings suggest that CsTST2 is a functional TST in cucumber, and lay a foundation for revealing the relationship of carbohydrate distribution and abiotic stress in the growth and development of cucumber.