Genome-wide identification, expression and functional analysis of sugar transporters in sorghum (Sorghum bicolor L.)

Sugar transporters are essential for osmotic process regulation, different signaling pathways and plant growth and development. Currently, few studies are available on the function of sugar transporter in sorghum. In this study, we performed a genome-wide survey of sugar transporter in sorghum (Sorghum bicolor L.). Totally 98 sorghum sugar transporters (SSTs) were identified via BLASTP. These SSTs classified into three families based on the phylogenetic and conserved domain analysis, including six sucrose transporters (SUTs), 23 sugars will eventually be exported transporters (SWEETs), and 69 monosaccharide transporters (MSTs). The sorghum MSTs were further divided into seven subfamilies including 24 STPs, 23 PLTs, two VGTs, four INTs, three pGlcT/SBG1s, five TMTs, and eight ERDs. Chromosomal localization of SST genes showed that they were randomly distributed on 10 chromosomes, and substantial clustering of them was evident on the specific chromosomes. Twenty-seven SST genes from the families of SWEET, ERD, STP, and PLT, were discovered to cluster in 8 tandem repeat event regions. Totally 22 SSTs comprising 11 paralogous pairs accounting for 22.4% of the entire genes, were located on the duplicated blocks. Different subfamily of SST proteins possessed the same conservative domain, but there are some difference in feature of motif and transmembrane helices (TMH). The publicly RNA-sequence data and real-time PCR revealed that SST genes exhibited distinctive tissue specific patterns. Functional studies showed that seven SSTs mainly located on the cell membrane and membrane organelles, and 14 selected SSTs could transport different types of monosaccharide in yeast. These findings will help us to further elucidate their roles in sorghum sugar transport and sugar signaling pathways.