Transcriptomic and Metabolomic Insights into the Enhanced Quality of Anoectochilus roxburghii Seedlings in Sugar-Free Versus Conventional Tissue Culture Systems

Background/Objective: Anoectochilus roxburghii, a high-value medicinal orchid, faces significant challenges in quality standardization during large-scale tissue culture due to a lack of understanding of the underlying molecular mechanisms. This study aimed to compare “Jianlan No.2” plantlets cultured under a conventional tissue culture system (CK) and a sugar-free tissue culture system (TD), to elucidate the phenotypic and molecular basis for quality improvement. Methods: A systematic comparison was conducted. Phenotypic traits of plantlets from both systems were measured. Integrated transcriptomic (RNA sequencing) and untargeted metabolomic analyses were employed to identify the molecular differences at the gene expression and metabolite accumulation levels. Results: TD-grown seedlings exhibited significantly superior growth characteristics, including greater plant height, higher rooting rate, and improved transplant survival. Transcriptomic analysis identified 416 differentially expressed genes (DEGs) (44 upregulated, 372 downregulated in TD), which were significantly enriched in pathways related to cell wall organization, apoplast, and photosynthesis. Sixteen key genes were pinpointed as closely associated with seedling growth and metabolic regulation. Metabolomic profiling revealed 502 differentially accumulated metabolites (DAMs), with significant perturbations primarily in phenylpropanoid biosynthesis and terpenoid metabolism. Conclusions: The sugar-free tissue culture system enhances A. roxburghii seedling quality by coordinately modulating photosynthetic capacity, carbon metabolism, and the biosynthesis of key secondary metabolites. These findings provide a crucial molecular foundation for optimizing tissue culture protocols and advancing the standardized, high-quality cultivation of this valuable medicinal plant.