Integrated Metabolomic and Transcriptomic Analyses Reveal Phenylpropanoid–Associated Variation Among Three Dendrobium huoshanense Germplasm Materials

Background: Dendrobium huoshanense flowers are a potentially valuable medicinal resource, but metabolic variation among different germplasm materials remains incompletely characterized. This study aimed to characterize metabolic and transcriptional differences among three D. huoshanense germplasm materials and to explore gene–metabolite associations related to phenylpropanoid metabolism. Methods: Untargeted LC–MS metabolomics and transcriptome sequencing were used to comparatively profile flowers of three D. huoshanense germplasm materials (DH-1, DH-2, and DH-3). Results: Metabolomic profiling detected 4357 metabolic features putatively assigned to 12 chemical classes and revealed clear separation among the three materials. A total of 1292, 1861, and 2035 differentially accumulated metabolic features were identified in DH-1 vs. DH-2, DH-1 vs. DH-3, and DH-2 vs. DH-3, respectively. Transcriptome analysis identified 33,665 expressed genes, including 3365, 5244, and 5964 DEGs in the respective pairwise comparisons. Phenylpropanoid biosynthesis was recurrently enriched across all three DEG comparisons. Exploratory gene–metabolite analysis identified associations involving phenylpropanoid–related candidate genes, including PAL, C4H, 4CL/4CL–like, HCT–like, CSE–like, COMT/OMT–like, and CAD, with the DH-2 vs. DH-3 comparison showing the most extensive molecular differences. Conclusions: The three D. huoshanense germplasm materials exhibited distinct metabolic and transcriptional profiles, providing candidate genes and metabolic features for subsequent targeted validation.