Sugar transporter OsSTP26 boosts rice tillering and yield through sugar accumulation

Transport and distribution of carbon assimilation products play a crucial regulatory role in rice growth, development, and yield formation. The importance of sugar transport proteins (STPs) in this process is being increasingly recognized. Here, we identified OsSTP26 as a critical regulator of tillering and yield in rice. OsSTP26, which is highly expressed in vascular bundles of leaf blades and leaf sheaths, encodes a plasma membrane-localized transporter with typical conserved sugar transporter domains. A hexose uptake assay in protoplasts demonstrated that OsSTP26 mediates transmembrane transport of glucose and fructose. Analyses of agronomic traits revealed that both knockout and overexpression of OsSTP26 increased tiller number and grain yield. Further physiological, transcriptomic, and hormone analyses indicated enhanced tillering through distinct mechanisms. Knockout of OsSTP26 increased glucose and sucrose levels in leaves and enhanced sugar unloading and sink cell uptake at the shoot base, leading to glucose and sucrose accumulation in the shoot base, thereby promoting tillering and grain yield through the HXK‑CK pathway. Overexpression of OsSTP26 elevated sucrose levels in leaves, enhanced sucrose phloem loading in source leaves to facilitate source-sink allocation, and consequently increased tillering and grain yield via the TOR‑nitrogen assimilation pathway. This study elucidates the mechanism by which OsSTP26 increases tillering and yield in rice.