Grafting joins a shoot, or scion, to a rootstock so growers can combine useful traits such as disease resistance, stress tolerance, productivity, and quality. Success, however, depends on a tightly timed healing sequence: cut surfaces must adhere, callus tissue must bridge the wound, and vascular connections must be restored. These steps can be unreliable in Fabaceae, the major crop family that includes soybean, cowpea, common bean, pea, lentil, chickpea, and alfalfa. Weak adhesion at the earliest stage can leave gaps or damaged layers that disrupt later tissue reunion, even between related species. Based on these challenges, there is a need to identify practical regulators that strengthen early graft adhesion in Fabaceae crops.
Researchers from Nagoya University, Kyoto University, and Huazhong Agricultural University published (DOI: 10.1093/hr/uhag095) the study in Horticulture Research on 13 March 2026. Using a high-throughput in vitro grafting (IVG) platform, the team screened a 3,000-compound library and identified graft-promoting molecule 1 (GPM1) as a graft-promoting molecule. They then evaluated its effects across four Fabaceae species, a cowpea–soybean heterograft, and two non-legume models, combining mechanical-force measurements, RNA sequencing (RNA-seq), quantitative reverse transcription polymerase chain reaction (qRT-PCR), root-response assays, and histological imaging to determine how the compound supports early graft union formation.
The researchers first reassembled cut stem segments of runner bean (Phaseolus coccineus) in custom IVG holders and measured the force required to separate them. The screening used mock-treated grafts as a negative control and 0.5 micromolar 2,4-dichlorophenoxyacetic acid (2,4-D) as a positive control. After four screening rounds, GPM1 was the only compound that consistently increased adhesion at five days after grafting (DAG), with a significant effect at 10 micromolar. The same treatment strengthened adhesion in cowpea (Vigna unguiculata), adzuki bean (Vigna angularis), and soybean (Glycine max), including cowpea scions grafted onto soybean rootstocks. GPM1 also increased adhesion in Nicotiana benthamiana and improved survival in Arabidopsis thaliana micrografts. Unlike 2,4-D, GPM1 neither inhibited primary-root growth nor activated a standard auxin-responsive reporter. RNA-seq at one DAG identified 64 differentially expressed genes (DEGs) after GPM1 treatment—49 upregulated and 15 downregulated—compared with 3,262 DEGs after 2,4-D treatment. The GPM1 response included the cell-wall-remodeling genes PvEXPA5, PvEXPA22, and PvEXPA25. In soybean grafts, qRT-PCR confirmed increased expression of Glyma.07G229000, a close homolog of PvEXPA5. Histological analysis showed a larger callus area caused by cell expansion rather than increased cell number, while treated soybean scions showed greater growth at 14, 21, and 28 DAG.
The authors said the study was designed around a practical question: whether a small molecule could help freshly cut plant tissues establish the physical contact required for later healing. They said the results indicate that GPM1 acts mainly during this early stage, encouraging cell-wall remodeling and allowing callus cells to expand across the graft interface. Its relatively focused molecular response differs from the broad cell-division program induced by 2,4-D. This distinction, the authors said, makes GPM1 useful both for studying graft biology and for developing strategies for difficult graft combinations.
GPM1 may eventually support more reliable grafting in legumes, where compatibility problems have restricted the use of rootstocks for disease control, stress resilience, seed multiplication, and the preservation of valuable hybrids. Its activity in phylogenetically distant plants also suggests that the underlying response may not be limited to Fabaceae. The evidence nevertheless supports an early-healing effect, not a proven increase in crop yield: in soybean self-grafts, survival and yield traits did not differ significantly from the control. The plant target that perceives GPM1 also remains unknown. Further nursery and field studies should test additional scion–rootstock combinations, delivery methods, effective doses, durability, safety, and crop-level benefits.
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References
DOI
10.1093/hr/uhag095
Original Source URL
https://doi.org/10.1093/hr/uhag095
Funding information
This work was supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (grant nos. 24K02043 and 25H01341 to Michitaka Notaguchi, and 22K06181 to Ken-ichi Kurotani); the Japan Science and Technology Agency (JST; grant no. JPMJTR194G to Michitaka Notaguchi); and the New Energy and Industrial Technology Development Organization (NEDO; project no. JPNP20004 to Michitaka Notaguchi). Qianqian Luo was supported by the JSPS Fellows program (grant no. 24KJ1276) and the Graduate Program of Transformative Chem-Bio Research (GTR) at Nagoya University, which is supported by Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) through the Doctoral Program for World-leading Innovative and Smart Education (WISE Program).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.