Characterization of the SWEET Gene Family in Longan ( Dimocarpus longan ) and the Role of DlSWEET1 in Cold Tolerance.

Sugars will eventually be exported transporters (SWEET), a group of relatively novel sugar transporters, that play important roles in phloem loading, seed and fruit development, pollen development, and stress response in plants. Longan ( Dimocarpus longan ), a subtropic fruit tree with high economic value, is sensitive to cold. However, whether the SWEET gene family plays a role in conferring cold tolerance upon longan remains unknown. Here, a total of 20 longan SWEET ( DlSWEET ) genes were identified, and their phylogenetic relationships, gene structures, cis -acting elements, and tissue-specific expression patterns were systematically analyzed. This family is divided into four clades. Gene structures and motifs analyses indicated that the majority of DlSWEETs in each clade shared similar exon-intron organization and conserved motifs. Tissue-specific gene expression suggested diverse possible functions for DlSWEET genes. Cis -elements analysis and quantitative real-time PCR (qRT-PCR) analysis revealed that DlSWEET1 responded to cold stress. Notably, the overexpression of DlSWEET1 improved cold tolerance in transgenic Arabidopsis , suggesting that DlSWEET1 might play a positive role in D. longan's responses to cold stress. Together, these results contribute to a better understanding of SWEET genes, which could serve as a foundation for the further functional identification of these genes.