The SWEET14 sugar transporter mediates mycorrhizal symbiosis and carbon allocation in Dendrobium officinale

Orchid mycorrhizal (OM) fungi form mutualistic relationships with orchids, facilitating the uptake of minerals from the soil in exchange for sugars and lipids provided by the plant. In this study, we explored the role of the DoSWEET14 sugar transporter in Dendrobium officinale during OM symbiosis. Transcriptome sequencing revealed significant changes in gene expression in mycorrhizal roots, particularly the upregulation of DoSWEET14. Subcellular localization studies confirmed that DoSWEET14 is localized to the plasma membrane, suggesting its involvement in nutrient exchange between the orchid and OM fungi. Complementation assays using a yeast strain deficient in hexose transport demonstrated that DoSWEET14 has broad substrate specificity, efficiently transporting multiple monosaccharides. Additionally, overexpression of DoSWEET14 in Arabidopsis increased sugar content without affecting biomass, supporting its role in carbohydrate transport and storage during symbiosis. These findings suggest that DoSWEET14 plays a key role in regulating carbon allocation and stabilizing the mutualistic relationship between Dendrobium officinale and OM fungi.