Identification and characterization of SWEET gene family in passion fruit reveals the involvement of PeSWEET3 in soluble sugar accumulation.

The sugars will eventually be exported transporters (SWEET) family is a class of sugar transporters that play crucial roles in plant growth, reproduction, and stresses response. The characteristics of 21 PeSWEETs, identified in passion fruit (Passiflora edulis Sims) and divided into four clades, were evaluated. Structural feature analysis showed that exon numbers ranged from 4 to 12, while motif 1, 2, and 3 were highly conserved. Analysis of RNA-seq from different tissues revealed that PeSWEETs showed tissue-specificity. Additionally, Cis-acting regulatory element analysis indicated that abundant hormone-response and stress response elements were enriched in promoters of PeSWEETs. Exogenous abscisic acid (ABA) treatment led to an increase in the soluble sugar accumulation and up-regulated the expression level of PeSWEET3. The PeSWEET3 protein localizes on the plasma membrane and exhibits transport activity of fructose, glucose, and mannose. Furthermore, ectopic expression of PeSWEET3 significantly enhanced soluble sugar accumulation in leaves of transgenic tobacco. Collectively, these results lay a solid foundation for further exploration on the role of PeSWEETs.