The sugar transporter AsSTL is regulated by the kinase Hog1 and is involved in glycerol transport and the response to osmotic stress in the salt-tolerant ascomycete aspergillus sydowii H-1

Abstract

Sugar transporters (STs) are critical biological macromolecules that involved in the regulation of fungal development and responses to abiotic stresses. While monosaccharide- and sucrose-specific transporters have been extensively characterized in yeast and plants, knowledge of STs in filamentous fungi remains limited. Here, through genome mining, we identified 173 STs in the salt-tolerant fungus Aspergillus sydowii H-1 and classified them into nine subgroups. Notably, 37 of these STs showed active responses to high-salt stress, with the glycerol transporter AsSTL exhibiting particularly strong induction. Protein–protein interaction analysis revealed that AsSTL is regulated by multiple mitogen-activated protein kinases, including Hog1, Ssk22, Ste11, Pbs2 and Fus3. Functional validation via Hog1 knockout experiments demonstrated that Hog1 positively regulates AsSTL. Localization studies revealed that AsSTL localizes to the plasma membrane, where it mediates glycerol absorption. The deletion of AsSTL significantly impaired glycerol uptake, conidial production, growth, and stress tolerance to NaCl and H₂O₂ stress, and purple pigment synthesis. These findings establish AsSTL as a key Hog1-reglulated protein, essential for glycerol homeostasis, salt stress adaptation, and secondary metabolite production in A. sydowii H-1. This study highlights the critical roles of ST proteins in fungal stress responses and provides insights into potential mechanisms for improving stress tolerance in fungi.