Molecular mechanisms of adventitious root formation in Sapium sebiferum: Insights from endogenous carbohydrate content analysis and transcriptome sequencing

Adventitious root (AR) formation is the primary bottleneck limiting the clonal propagation of Sapium sebiferum , a multi-purpose tree with high-value seed oil and medicinal metabolites. Here, we integrated morpho-anatomical profiling, endogenous carbohydrate dynamics and high-resolution transcriptomics to uncover the molecular framework underlying AR induction by the synthetic auxin 1-naphthaleneacetic acid (NAA). Four developmental checkpoints (0, 7, 14 and 21 d after cutting, DAC) were resolved, revealing that NAA triggered a “mixed” rooting pattern originating from both callus and vascular cambium. During the early induction phase, starch was rapidly hydrolyzed, leading to a > 2-fold increase in soluble sugars that fuelled primordium initiation; this metabolic switch persisted until 21 DAC. RNA-seq identified 6991 differentially expressed genes (DEGs) across rooting stages, with the induction stage exhibiting the largest transcriptional reprogramming (3963 DEGs). Weighted gene co-expression network analysis (WGCNA) pinpointed a turquoise module positively correlated with starch content and a blue module associated with soluble sugars, together harbouring 62 core genes of the starch/sucrose metabolism pathway. Among these, ten hub genes—including glgC , otsB , TPS , BMY and bglB —were proposed as key regulators linking auxin-driven signalling to carbohydrate reallocation. qRT-PCR validated the expression dynamics of nine hub genes (R² ≥ 0.83). We propose a stage-specific model in which NAA accelerates AR formation through transcriptional reprogramming of carbon partitioning, providing gene targets to overcome rooting recalcitrance in S. sebiferum and other hardwood species. • NAA promotes adventitious rooting via mixed-type ontogeny in Sapium sebiferum cuttings. • Sustained starch-to-sugar conversion fuels primordium initiation and root elongation. • WGCNA identifies ten carbon-reallocation hubs ( glgC , otsB , TPS , BMY , bglB ); qPCR validates R² ≥ 0.83. • Stage-specific “auxin-sugar-rooting” model offers gene targets to overcome rooting recalcitrance in hardwood species.