The Green Revolution of the 20 th century transformed global wheat production, largely through the introduction of semi-dwarfing genes that reduced plant height, minimized lodging risk, and allowed for more nitrogen fertilizer use. Yet modern breeding remains heavily dependent on a limited set of these genes, some of which carry trade-offs in early seedling vigour, grain filling, and nitrogen-use efficiency.
Now, international research teams led by China Agricultural University and the Chinese Academy of Agricultural Sciences have identified and cloned a new semi-dwarfing gene, Sdd1 ( semi-dwarf and dense-spike 1 ), that modulates plant height and spike architecture through a distinct hormonal balancing mechanism—offering breeders a fresh genetic resource to fine-tune wheat architecture.
The work builds on the team’s 2023 Nature report (Song et al., 2023, Nature. 617:118-124), which described a naturally occurring r-e-z large fragment deletion haploblock that promotes compact, semi-dwarf growth by rebalancing brassinosteroid and gibberellin signalling. In the new study, the researchers set out to find additional dwarfing genes operating independently of the r-e-z deletion background. Their search led them to AS34, a somatic mutant derived from the wheat line Lankao 906 (LK906, also known as Yumai 66), which harbors the r-e-z deletion haploblock.
In field trials, AS34 plants were just 45 cm tall on average—a notable 41.6% reduction compared with the 77 cm height of the wild-type LK906. In particular, the mutant’s spike length reduced by 44.0%, while spikelet density surged by 60.3%. Microscopic analysis revealed that stem cells in AS34 were shorter and broader than those in LK906, pointing to reduced longitudinal cell elongation as the cellular basis for the dwarf phenotype.
Genetic dissection placed the semi-dwarf and dense-spike traits under the control of a single major locus on chromosome 3B. Through fine-mapping with a segregating population, whole-genome resequencing, and newly developed molecular markers, the team pinpointed Sdd1 to a 5.7-Mb interval and identified TraesCS3B02G260400 , encoding a small protein with function yet to be characterized, as the prime candidate gene. Independent mutant lines carrying distinct lesions in this gene—in the Jing 411 genetic background—all showed alterations in plant height and spike development, providing strong genetic confirmation of Sdd1 ’s regulatory role.
Hormone response assays added another layer of insight. Unlike LK906, AS34 showed enhanced sensitivity to gibberellin and auxin. This pattern suggests that Sdd1 does not act through a single hormone pathway but rather orchestrates cross-talk among multiple growth-regulating signals—a feature that may help decouple height reduction from negative side effects.
“Our earlier work demonstrated that the r-e-z fragment deletion improves plant architecture, increases grain weight, and boosts yield, mainly through the modulation of brassinosteroid and gibberellin,” says corresponding author of the study, Professor Jie Liu from China Agricultural University. “By identifying and cloning Sdd1 —which remains fully functional in the r-e-z -deleted background—we’ve expanded the molecular framework for understanding how dwarfing genes wire into wheat developmental networks.”
Liu further elaborates on the distinct mechanism uncovered in this study, “What excites us is that, while the r-e-z deletion primarily influences brassinosteroid and gibberellin pathways, Sdd1 integrates multiple hormone signals in a more complex manner.”
The researchers further observed that AS34 mutants show dramatically reduced sensitivity to brassinosteroid but enhanced responses to both gibberellin and auxin. “This distinctive hormonal signature suggests Sdd1 occupies a unique node in the plant’s growth regulatory network,” adds Liu.
This feature may be particularly valuable for wheat breeding because it could help break the negative correlations that often accompany height reduction, such as reduced grain filling or compromised seedling vigor, usually caused by the largely blocked gibberellin signaling transduction.
“One of the most important aspects of this discovery is that Sdd1 remains fully functional in the r-e-z -deleted background,” emphasizes Liu. “This means we’ve identified a gene that can additively or synergistically interact with existing dwarfing resources.”
For breeders, this opens up new possibilities for stacking beneficial alleles to achieve optimal plant architecture without the trade-offs that have constrained the use of our current dwarfing gene toolbox.
Looking ahead, Liu outlines the next steps for the research, “We are only at the beginning of understanding its full potential. The protein encoded by TraesCS3B02G260400 is small and its molecular function remains to be characterized. We are now focusing on deciphering its mechanistic details—how it perceives or transmits hormonal signals, and what downstream target components it regulates.”
“Cloning Sdd1 is just the first step. Considerable work lies ahead to decipher its molecular function and clarify how it regulates growth and development,” adds Professor Xingguo Ye from the Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, who co-led the research. “We are now focused on evaluating its practical breeding potential across different genetic backgrounds and environments to determine how broadly useful this gene might be for wheat improvement worldwide.”
The study also benefited from conceptual guidance and manuscript preparation input from Professors Qixin Sun and Zhongfu Ni from China Agricultural University. “With Sdd1 now in hand, breeders have a promising new entry point for designing wheat varieties that strike an optimal balance between height reduction, spike compactness, and overall productivity—without the constraints of the current dwarfing-gene toolbox,” says Ni.
###
Contact contacts:
Professor Jie Liu
China Agricultural University
Professor Xingguo Ye
Institute of Crop Sciences, Chinese Academy of Agricultural Sciences
The publisher KeAi was established by Elsevier and China Science Publishing & Media Ltd to unfold quality research globally. In 2013, our focus shifted to open access publishing. We now proudly publish more than 200 world-class, open access, English language journals, spanning all scientific disciplines. Many of these are titles we publish in partnership with prestigious societies and academic institutions, such as the National Natural Science Foundation of China (NSFC).
The Crop Journal
Experimental study
Not applicable
Map-based cloning and functional analysis of the semi-dwarf and dense-spike gene Sdd1 in bread wheat
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.