Asparagus cochinchinensis (Lour.) Merr. is a classic medicinal and edible homologous plant with rapidly growing market demand, yet the molecular mechanism underlying the biosynthesis of its core active steroidal components remains largely unknown, and the lack of high-quality genome references severely hinders its molecular breeding and quality improvement. We constructed the first full-length transcriptome of Asparagus cochinchinensis (root tuber, stem, phylloclade) via PacBio SMRT and Illumina sequencing, and integrated widely targeted metabolomics to investigate the molecular basis of tissue-specific accumulation of steroidal components. A total of 1299 metabolites were identified, with steroidal markers diosgenin and stigmasterol accumulating significantly higher in aerial tissues than in underground root tubers. We obtained 106165 high-quality unigenes (94.5% annotation rate) and found differentially expressed genes enriched in photosynthesis, glycolysis, and phenylpropanoid biosynthesis across tissues. The biosynthetic pathway for steroidal components was fully mapped, identifying 40 full-length enzyme-encoding genes, most showing higher expression in aerial tissues, consistent with metabolite accumulation patterns. Furthermore, 15 members of the HMGR gene family (the first rate-limiting enzyme in the MVA pathway) were systematically identified from the transcriptome. Molecular docking revealed AcHMGR1 had the highest binding affinity for the cofactor NAD(P)H. Heterologous overexpression of AcHMGR1 in Nicotiana benthamiana significantly enhanced HMGR enzyme activity (1.42-fold of wild type) and markedly increased total phytosterol accumulation (12.24-fold of wild type), particularly β -sitosterol (7.88-fold of wild type), the direct precursor of diosgenin. qRT-PCR validated the transcriptome data reliability. This study provides the first high-quality full-length transcriptome reference for A. cochinchinensis , uncovers the transcriptional basis of tissue-specific steroidal metabolic differences, and confirms AcHMGR1 as a key positive regulator of phytosterol biosynthesis, offering valuable genetic targets for its molecular breeding and quality improvement.
Zhang et al. (Mon,) studied this question.