Genome-Wide Identification, Expression, and Functional Analysis of the Sugar Transporter Gene Family in Cassava (Manihot esculenta).

The sugar transporter () gene family encodes monosaccharide transporters that contain 12 transmembrane domains and belong to the major facilitator superfamily. genes play critical roles in monosaccharide distribution and participate in diverse plant metabolic processes. To investigate the potential roles of in cassava () tuber root growth, genome-wide identification and expression and functional analyses of the gene family were performed in this study. A total of 20 genes (-) containing the Sugar_tr conserved motifs were identified from the cassava genome, which could be further classified into four distinct groups in the phylogenetic tree. The expression profiles of the genes explored using RNA-seq data showed that most of the genes exhibited tissue-specific expression, and 15 out of 20 genes were mainly expressed in the early storage root of cassava. qRT-PCR analysis further confirmed that most of the displayed higher expression in roots after 30 and 40 days of growth, suggesting that these genes may be involved in the early growth of tuber roots. Although all the MeSTP proteins exhibited plasma membrane localization, variations in monosaccharide transport activity were found through a complementation analysis in a yeast () mutant, defective in monosaccharide uptake. Among them, MeSTP2, MeSTP15, and MeSTP19 were able to efficiently complement the uptake of five monosaccharides in the yeast mutant, while MeSTP3 and MeSTP16 only grew on medium containing galactose, suggesting that these two MeSTP proteins are transporters specific for galactose. This study provides significant insights into the potential functions of in early tuber root growth, which possibly involves the regulation of monosaccharide distribution.