Chemical screening in Fabaceae identified GPM1 as a novel compound enhancing early graft adhesion

Plant grafting is a horticultural technique used to join different plants with desirable traits. However, graft incompatibility limits its application, especially in agriculturally important Fabaceae species. To enhance grafting efficiency, we conducted chemical screening utilizing an in vitro grafting (IVG) system in Fabaceae. In this study, we screened 3000 artificial chemical compounds and identified a compound, designated graft-promoting molecule 1 (GPM1), which enhanced graft adhesion in Fabaceae species-including Phaseolus coccineus, Vigna unguiculata, Vigna angularis, and Glycine max-as well as in V. unguiculata/G. max hetero-IVGs at 5 days after grafting (DAG). Notably, GPM1 also increased adhesive force in Nicotiana benthamiana IVGs and improved survival rates in Arabidopsis thaliana micrografting, indicating that its activity is not restricted to Fabaceae. Transcriptome analysis of P. coccineus IVGs at 1 DAG revealed that application of GPM1 induced the upregulation of cell wall modification genes, including PvEXPA5, PvEXPA22, and PvEXPA25. In contrast, treatment with 2,4-dichlorophenoxyacetic acid (2,4-D) induced a broader transcriptional response, predominantly upregulating genes related to cell division. In G. max stem grafting, GPM1 enhanced scion growth and promoted the formation of larger callus cells at the graft junction. Moreover, qRT-PCR analysis revealed that GPM1 significantly upregulated Glyma.07G229000, a homolog of PvEXPA5. The upregulation of cell wall-associated genes by GPM1 is consistent with a role in early graft union formation, potentially by facilitating tissue adhesion at the graft interface. Collectively, this study identifies GPM1 as a chemical regulator that enhances graft adhesion and provides insight into molecular processes associated with early graft adhesion.