The SlSWEET12c Sugar Transporter Promotes Sucrose Unloading and Metabolism in Ripening Tomato Fruits

Sugar content is a primary determinant of taste and quality in tomato (Solanum lycopersicum) fruit. Sugar allocation from source to sink is dependent on the activity of plasma membrane sugar transporters and is a critical process in plant development. Sugar will eventually be exported transporters (SWEETs) are sugar transporters that play key roles in plant biology, including growth and development. However, few studies have been conducted on the tomato SWEET protein family to date. Through gene expression analysis, we found that SlSWEET12c had the highest expression during the red ripening stage of tomato fruits. Yeast functional complementation, subcellular localization, and GUS activity assays showed that SlSWEET12c is a plasma membrane-localized sugar transporter that accumulates in the vascular bundles, carpel, and sarcocarp. Silencing SlSWEET12c increased sucrose accumulation and reduced the number of hexoses in tomato fruits; the opposite effects were observed under SISWEET12c overexpression. Invertase activity was also decreased after silencing SISWEET12c. These results suggest that SlSWEET12c is a sugar transporter that promotes sucrose unloading and metabolism in ripening tomato fruits, offering a new target for improving tomato quality and production.