Identification of MFS gene family in tomato and functional characterization of SlZIF1/SlMFS4 under salt stress

Abiotic stresses, particularly salinity, significantly impair crop productivity and ecological stability. The Major Facilitator Superfamily (MFS), a ubiquitous group of secondary metabolites' transporters critical for cellular homeostasis, plays vital roles in nutrient uptake, ion balance, and stress adaptation across organisms. Here, we identified 245 MFS genes in tomato, classified into 11 subfamilies, with the MFS-1 subfamily selected for comprehensive analysis. Transcriptomic and qRT-PCR analyses demonstrated that MFS-1 genes exhibited spatiotemporal expression dynamics in various tissues and under abiotic stresses, with SlZIF1/SlMFS4 (homologous to ZINC-INDUCED FACILITATOR1 in Arabidopsis, AtZIF1) showing pronounced upregulation under salinity. Functional validation via transgenic tomato overexpression revealed that SlZIF1/SlMFS4 enhances salt tolerance by improving chlorophyll retention, proline biosynthesis, antioxidant enzyme activity, and Na⁺/K⁺ homeostasis, while mitigating ROS accumulation. Furthermore, the luciferase complementation imaging assays identified interactions with stress-responsive proteins (Sl14-3-3s and SlSOS2). This study advances the understanding of MFS evolution in tomato and provides genetic targets for improving salt tolerance in crops, addressing global agricultural challenges posed by saline soils.