Functional Studies and Expression Characteristics of the Vacuolar Sugar Transporter CoSWEET2a in Camellia oleifera

Sugar transporters of the SWEET family are essential for plant growth, development, yield formation, and stress responses by regulating sugar transport and distribution. This study characterizes the function and expression characteristics of CoSWEET2a, a Clade I SWEET gene in <i>Camellia oleifera</i>. We conducted subcellular localization, functional complementation in <i>Arabidopsis</i>, sugar response assays, drought tolerance tests, and hormone induction analysis. A key finding is <i>CoSWEET2a</i>, which that is localized on the vacuolar membrane in <i>Camellia oleifera</i>. Heterologous expression in <i>Arabidopsis atsweet2</i> mutants revealed sugar-specific effects on root growth. Moreover, expression of <i>CoSWEET2a</i> increased soluble sugar content in <i>Arabidopsis</i> seeds. Additionally, <i>CoSWEET2a</i> overexpression enhanced drought stress tolerance by augmenting sugar content. The expression of <i>CoSWEET2a</i> is regulated by gibberellin (GA) and abscisic acid (ABA), and its promoter contains corresponding hormone response elements. In conclusion, CoSWEET2a functions as a "sugar buffer" on the vacuolar membrane, regulating sugar accumulation, root development, and drought stress responses. This discovery not only reveals that vacuolar SWEET plays an important role in maintaining cytoplasmic sugar homeostasis in plants but also provides a direct genetic target for engineering high-quality, drought-tolerant crops.