The hexose transporters CsHT3 and CsHT16 regulate postphloem transport and fruit development in cucumber.

This article investigates the roles of hexose/H+ symporters CsHT3, CsHT12, and CsHT16 in postphloem sugar transport and fruit development in cucumber (Cucumis sativus L.). The study identifies 16 hexose transporter (CsHT) genes in cucumber, with CsHT3, CsHT12, and CsHT16 highly expressed in fruits and localized to the plasma membrane of phloem-specific cells, shifting from sieve element–companion cells to phloem parenchyma during fruit development. Functional analyses, including gene knockout and overexpression, reveal that CsHT16 knockout mutants produce shorter but thicker fruits with altered sugar and hormone homeostasis, while simultaneous downregulation of CsHT3/12/16 reduces fruit size and sugar content; conversely, CsHT3 overexpression increases fruit size and sugar levels. These findings support a model where CsHT3, CsHT12, and CsHT16 mediate hexose uptake from the apoplast into phloem parenchyma cells, completing postphloem sugar unloading and regulating carbohydrate supply essential for cucumber fruit enlargement.