Genome-Wide Identification of the SWEET Gene Family and Functional Analysis of LpSWEET13 in Perennial Ryegrass Under Drought Stress

SWEETs (Sugars Will Eventually be Exported Transporters) represent a distinct category of proteins responsible for mediating intracellular sugar transport. These transporters are involved in sugar allocation processes, contribute to plant growth and development, and mediate adaptive responses to abiotic and biotic stresses. Despite extensive research on SWEET genes in many plant species, their functions in perennial ryegrass have not been clearly characterized. In this study, genome-wide bioinformatic analyses were conducted to identify SWEET family members in perennial ryegrass (Lolium perenne; LpSWEETs) and to explore their potential involvement in drought stress responses. Twenty-three LpSWEET genes were identified based on whole-genome sequence data, and phylogenetic inference indicated that these genes clustered into four clades. Comprehensive analyses of gene organization, conserved motifs, cis-regulatory elements, and protein features demonstrated strong evolutionary conservation across LpSWEET members, while quantitative real-time PCR analysis demonstrated that LpSWEET13 exhibited drought-responsive expression, and subcellular localization analysis showed that LpSWEET13 was localized in the plasma membrane. Under drought stress, transgenic Arabidopsis thaliana lines overexpressing LpSWEET13 presented a substantially higher survival rate than their corresponding wild-type controls. In addition, ectopic expression of LpSWEET13 increased expression levels of AtP5CS1, AtRD22, AtRD29A, and AtRD29B expression. These findings offer insights into the cladistic characteristics of the LpSWEET family and establish a useful framework for subsequent functional studies of LpSWEET genes.