KEY MESSAGE: Transcriptome analysis identified the hub gene SmNDUFS4, which promotes graft union formation in Sapindus mukorossi by accelerating callusproliferation and vascular reconnection, thereby enhancing grafting efficiency. Grafting is widely employed to shorten the seedling stage and enhance fruit quality, while theoretically serving as a model for studying the transport and rearrangement of genetic material. Despite grafted plants exhibiting superior characteristics in multiple aspects, the underlying healing mechanisms remain poorly understood. This study identified four critical phases: isolation layer formation, callus proliferation (7 DAG), cambial bridge establishment (14-30 DAG), and vascular reconnection (after 30 DAG). Subsequently, transcriptome sequencing was performed on ten sample groups from two tissues (scion and rootstock) across five developmental stages. Analysis based on GO, KEGG, WGCNA, and correlation studies identified the key candidate gene SmNDUFS4. Genetic engineering established Arabidopsis transgenic lines overexpressing 35S::SmNDUFS4. Functional validation in Arabidopsis showed that SmNDUFS4 overexpression significantly accelerated cell division at the graft interface and enhanced vascular continuity. Transcriptome sequencing findings corroborated morphological observations, indicating that SmNDUFS4 overexpression promotes graft union formation by modulating plant stress responses. This study provides the first dynamic characterization of the graft union formation process in S. mukorossi and identifies SmNDUFS4 as a key gene in graft union formation. It establishes a crucial foundation for mechanistic research into graft union formation in S. mukorossi and offers a potential biotechnological strategy for enhancing grafting efficiency in woody plants.
Wang et al. (2026) studied this question.