The sugar transporter system of strawberry: genome-wide identification and expression correlation with fruit soluble sugar-related traits in Fragaria × ananassa Duchesne germplasms collection

Strawberry (Fragaria × ananassa Duchesne) is an important crop worldwide and appreciated for its unique fruit flavor. The involvement of MFS sugar transporters (STs) in cultivated strawberry fruit sugar accumulation is largely unknown. In this work, we characterized the genetic variation associated with fruit soluble sugars in a collection including 154 cultivars. Then, a total of 67 ST genes were identified in the v4.0 genome integrated with the v4.0.a2 protein database of F. vesca, the dominant subgenome provider for modern cultivated strawberry. Phylogenetic analysis updated the nomenclature of strawberry ST homeologs. Both the chromosomal distribution and structural characteristics of the ST family were improved. Semi-RT-PCR analysis in nine tissues from 'Benihoppe' screened 34 highly expressed ST genes in fruits. In three cultivars with dramatically differing fruit sugar levels, qPCR integrated with correlation analysis between ST transcript abundance and sugar content identified 13 sugar-correlated genes. The correlations were re-evaluated across 19 cultivars, including major commercial cultivars grown in China. Finally, a model of the contribution of the sugar transporter system to subcellular sugar allocation in strawberry fruits was proposed.