Hormonal and transcriptomic signatures of scion-associated early growth suppression in Camellia oleifera

Abstract Background Camellia oleifera is widely propagated by grafting in China, yet the elite cultivar ‘Changlin 53’ consistently shows minimal shoot growth in the first year after grafting across multiple rootstock genotypes, constraining nursery production. This slow-growth phenotype has been previously reported, but the graft-interface processes associated with it remain poorly understood. To investigate these processes, we compared graft healing in CL53 scions with fast-growing ‘Changlin 18’ scions on a common CL18 half-sib rootstock. Results Histology, hormone profiling, and transcriptome sequencing across five post-grafting stages revealed that CL53 showed delayed callus organization and vascular reconnection despite sharing the rootstock background. Growth and biomass analysis showed that CL18/CL53 seedlings had significantly lower seedling height, shoot fresh weight, and shoot dry weight, and significantly higher fresh and dry root/shoot ratios than CL18/CL18. In contrast, ground diameter, root fresh weight, and root dry weight did not differ significantly. For root morphological traits, CL18/CL53 had significantly lower total root length but significantly larger average root diameter than CL18/CL18, while root surface area and root volume did not differ significantly. MapMan analysis revealed stage-specific transcriptional reprogramming, including early suppression of cell cycle-related genes; mid-stage metabolic and defense imbalance; mid-to-late activation of ERF stress-responsive genes with downregulation of Hsp70/Hsp90 , small HSP, and protein quality control genes; and late upregulation of phenylpropanoid metabolism and DOF transcription factors, with specific BBX genes also upregulated. CL18/CL53 exhibited more stage-specific and less temporally coordinated differential expression than CL18/CL18. Hormone profiling further revealed genotype-dependent differences in the timing of auxin, cytokinin, jasmonate, salicylic acid, and ABA dynamics during graft healing. Candidate genes such as CYP86A22 and cell wall-remodeling genes including PME12 , PME20 , and PME41 emerged as potential links between hormone signals and delayed interface remodeling.Consistent with previous reports and unpublished production observations, this slow-growth phenotype was scion-associated under the tested rootstock background. Conclusions These findings suggest that the previously reported early growth suppression in CL53 is associated with a prolonged wound-responsive state and a delayed transition to regenerative growth at the graft interface, rather than to classical graft incompatibility. The altered root architecture, characterized by shorter but thicker roots, together with elevated root-to-shoot ratios, further indicates a shift in biomass allocation associated with delayed interface reconstruction. We propose a working model in which this delay contributes to the reduced early vigor of CL53 scions.