Population growth, climate change, and shrinking arable land are placing increasing pressure on global food production. Rice ( Oryza sativa L.) is a staple food for nearly half of the world’s population; increasing its yield is essential for safeguarding global food security.
Productive tiller number is a major yield component because each productive tiller can develop into a grain-bearing panicle. Tiller growth depends on the movement of photoassimilates from source leaves to axillary buds and the shoot base. Although sugar transporters help regulate this source-to-sink carbon flow, the functions of many rice sugar transport proteins remain unclear.
A research team led by Professor Zhenhua Zhang and Dr. Mingjuan Li at Hunan Agricultural University and Yuelushan Laboratory found that the rice sugar transporter OsSTP26 plays a key role in regulating tillering. They found that both knockout and overexpression of OsSTP26 increased tiller number and grain yield, but through distinct sugar-signaling pathways. Overall, the study identifies OsSTP26 as an important link between source-to-sink carbon allocation and tiller development in rice.
The findings were made available in The Crop Journal .
The researchers found that OsSTP26 is highly expressed in the vascular bundles of rice leaf blades and leaf sheaths during tillering. Localization and rice protoplast assays indicated that OsSTP26 functions as a plasma membrane transporter for glucose and fructose. To determine its role in rice growth, the team generated two CRISPR/Cas9 knockout lines and two overexpression lines in the japonica cultivar Taipei 309.
“Both knockout and overexpression increased tiller number and grain yield,” shares Qidong Zhu, co-first author of the study. “Across two years of field experiments, the knockout lines showed increases of 23.6%-24.8% in productive tiller number and 13.2%-21.7% in grain yield per plant.”
Corresponding increments in the overexpression lines were 24.8%-50.4% and 16.3%-37.9%, respectively, while grain number per panicle and thousand-grain weight remained largely unchanged, indicating that yield gains were driven primarily by an increase in productive tillers.
“Finding that both OsSTP26 knockout and overexpression increased tiller number was unexpected,” says Zhu. “We performed physiological and molecular analyses and found that the two genetic changes converged on the same yield-related phenotype, but they did so through different sugar-signaling pathways”.
Notably, in the knockout lines, glucose and sucrose accumulated in the leaves and shoot base, together with increased expression of genes involved in sugar unloading and sink-cell uptake. “At the shoot base, greater sugar availability was accompanied by changes in OsHXK1 and cytokinin-related gene expression and by increased levels of the active cytokinins cis-zeatin and N6-isopentenyladenine,” says Zhu.
These findings support the involvement of the HXK–cytokinin pathway in promoting tiller-bud outgrowth. In contrast, OsSTP26 overexpression increased sucrose accumulation and upregulated OsSUT and OsSWEET genes involved in sucrose loading, consistent with enhanced source-to-sink carbon transport. It also upregulated TOR and genes associated with nitrogen uptake, transport, and assimilation, while increasing total nitrogen in the shoot base. Together, these results suggest that OsSTP26 overexpression coordinates sucrose supply with TOR-associated nitrogen metabolism to support tiller growth.
“Two years of field experiments confirmed that increased productive tiller number was accompanied by higher grain yield,” says Professor Zhenhua Zhang, co-corresponding author of the study. “However, the 2.3%–5.7% reduction in seed-setting rate in the overexpression lines shows that OsSTP26 expression would need to be carefully optimized for breeding applications.”
By showing that altered expression of a single sugar transporter can engage distinct sugar-signaling pathways, this study expands current understanding of how carbon allocation, hormone signaling, and nitrogen metabolism are coordinated during tiller growth. It also provides a basis for evaluating OsSTP26 as a potential target for high-yield rice breeding.
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Author contact:
Zhenhua Zhang, zhzh1468@163.com.
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The Crop Journal
Experimental study
Not applicable
Sugar transporter OsSTP26 boosts rice tillering and yield through sugar accumulation
The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this article.