Genome-wide identification and expression analysis of the SiSWEET gene family in Setaria italica and functional characterization of the SiSWEET13a in Arabidopsis.

Sugar will eventually be exported transporters (SWEETs), an original family of sugar transporters that facilitate the cell membrane flux traversing and govern long-distance sugar distribution throughout plant development. SWEETs playvital roles in various developmental processes including phloem loading, pollen nutrition, seed filling, and pathogen nutrition. Although the SWEET family has been systematically reported in different organisms, research on foxtail millet (Setaria italica L.) has not been reported. In this study, 24 SiSWEETs were identified in the foxtail millet genome using bioinformatics analysis and were divided into four groups. Chromosome mapping showed that SiSWEETs were distributed on seven chromosomes, the size of the encoded amino acids ranged between 231 and 320, the SiSWEETs all contained the Sugar_tr (PF03083) conserved domain, and five conserved motifs were identified. Cis-acting elements in the SiSWEET promoter region showed light-response elements in all genes, and most genes were hormone- and stress-response elements. Expression profile analysis demonstrated that SiSWEET13a had considerably high leaf top 2-3 expression after heading, and responded to exogenous sucrose. Subcellular localization analysis revealed that SiSWEET13a was localized to the plasma membrane. SiSWEET13a overexpression promoted growth and decreased the starch and sugar contents of leaves in transgenic A. thaliana, and the starch accumulation phenotype was partially complemented by SiSWEET13a overexpression in the double mutant. Y2H and BiFC assays demonstrated that SiSWEET13a interacts with G protein receptors (GPR107) and aquaporin (PIP1). These findings provide a comprehensive characterization of SWEET genes in Setaria italica and offer insights into the biological functions of SiSWEET13a in plant growth and development.