GhSWEET15-3A/3D regulates yield and fiber quality via orchestrating sugar distribution between cotton seeds and fibers

Cotton ( Gossypium hirsutum ) is a globally important crop cultivated for its fiber and cottonseed. The distribution of sugars between seeds and fibers is a critical determinant of cotton yield and fiber quality. However, the molecular mechanisms underlying sugar distribution remain poorly understood. In this study, we investigated the role of GhSWEET15–3A/3D , a member of the Sugars Will Eventually be Exported Transporter (SWEET) gene family, in sugar distribution during cotton development. GhSWEET15–3A/3D is specifically expressed in ovules and fibers, and its knockout via CRISPR-Cas9 resulted in a significant increase in soluble glucose content in ovules but a decrease in fibers. This disruption of sugar led to embryo developmental arrest, reduced yield traits, and impaired fiber quality in ghsweet15 mutants. Conversely, overexpression of GhSWEET15–3A/3D produced smaller seeds, longer fibers, and a higher lint percentage. Promoter activity analysis identified a core regulatory region (−337 bp to −597 bp) essential for GhSWEET15–3A/3D expression in seeds. Further, co-expression analysis and yeast one-hybrid (Y1H) assays demonstrated that the B3-type transcription factor GhABI3 binds to the "TTGCATGGA" cis-element within this region, linking GhSWEET15–3A/3D regulation to ABA signaling. Collectively, these findings reveal that GhSWEET15–3A/3D , under the control of GhABI3, orchestrates soluble sugar flow between the embryo, endosperm, and fiber, ultimately influencing cotton yield and fiber quality. This study provides novel insights into the molecular mechanisms of sugar distribution in cotton and highlights potential targets for genetic improvement. • GhSWEET15–3A/3D is a key regulator of photoassimilate allocation to embryo, essential for normal seed development in cotton. GhSWEET15–3A/3D balances sugar allocation between cotton seeds and fibers, pivotal for yield and fiber quality. • GhABI3-GhSWEET15–3A/3D module is a promising target for enhancing yield and fiber quality, particularly under adversity.